Want to create WPF solution in MVVM pattern

Normally I would ask you to post code before helping as we are not here to write your code for you. However, I will make an exception to get you started.

The key to the MVVM Design Pattern is Data Binding. You can read more about it in detail here: Data Binding Overview | Microsoft Docs[^]

The second part of your question is about XAML Triggers ... Do this when this happens. This is called an Event Trigger. You can learn more about Triggers here: Styling and Templating | Microsoft Docs[^]

Also, a good learning resource for WPF is: Welcome - The complete WPF tutorial[^] and for MVVM there are many resources to learn from: wpf mvvm tutorial - Google Search[^]

Here is a working example based on your question...

For data binding, here are a couple of base classes for Data Binding:

public abstract class ObservableBase : INotifyPropertyChanged
{
    public void Set<TValue>(ref TValue field, TValue newValue, [CallerMemberName] string propertyName = "")
    {
        if (!EqualityComparer<TValue>.Default.Equals(field, default(TValue)) && field.Equals(newValue)) return;
        field = newValue;
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    public event PropertyChangedEventHandler PropertyChanged;
}


public abstract class ViewModelBase : ObservableBase
{
    public bool IsInDesignMode
        => (bool) DesignerProperties.IsInDesignModeProperty
            .GetMetadata(typeof(DependencyObject))
            .DefaultValue;
}

Next the ViewModel:

public class MainViewModel : ViewModelBase
{
    public MainViewModel()
    {
        if (IsInDesignMode)
        {
            // design time only...
            valueA = 5;
            valueB = 6;
            Calc();
        }
        else
        {
            // runtime only...
        }
    }

    #region Properties

    private int valueA;
    public int ValueA
    {
        get => valueA;
        set
        {
            Set(ref valueA, value);
            Calc();
        }
    }

    private int valueB;
    public int ValueB
    {
        get => valueB;
        set
        {
            Set(ref valueB, value);
            Calc();
        }
    }

    private int valueC;
    public int ValueC
    {
        get => valueC;
        set => Set(ref valueC, value);
    }

    private int valueD;
    public int ValueD
    {
        get => valueD;
        set => Set(ref valueD, value);
    }

    #endregion

    #region Methods

    private void Calc()
    {
        ValueC = valueA + valueB;
        ValueD= valueA * valueB;
    }

    #endregion
}

And lastly, the View:

<Window x:Class="WpfMvvmSimple.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:l="clr-namespace:WpfMvvmSimple"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">

    <Window.DataContext>
        <l:MainViewModel/>
    </Window.DataContext>

    <Grid HorizontalAlignment="Center" VerticalAlignment="Center">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition Width="Auto"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition/>
            <RowDefinition/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <Grid.Resources>
            <Style TargetType="TextBlock">
                <Setter Property="VerticalAlignment" Value="Center"/>
            </Style>
            <Style TargetType="TextBox" x:Key="TextBox">
                <Setter Property="VerticalContentAlignment" Value="Center"/>
                <Setter Property="Margin" Value="10"/>
                <Setter Property="Width" Value="100"/>
                <Setter Property="Height" Value="25"/>
                <Setter Property="Grid.Column" Value="1"/>
                <Style.Triggers>
                    <Trigger Property="IsMouseOver" Value="True">
                        <Setter Property="Background" Value="Silver" />
                    </Trigger>
                </Style.Triggers>
            </Style>
            <Style TargetType="TextBox" x:Key="TextBoxA" BasedOn="{StaticResource TextBox}">
                <Style.Triggers>
                    <Trigger Property="IsMouseOver" Value="True">
                        <Setter Property="Background" Value="LightBlue" />
                    </Trigger>
                </Style.Triggers>
            </Style>
            <Style TargetType="TextBox" x:Key="TextBoxB" BasedOn="{StaticResource TextBox}">
                <Style.Triggers>
                    <Trigger Property="IsMouseOver" Value="True">
                        <Setter Property="Background" Value="LightGreen" />
                    </Trigger>
                </Style.Triggers>
            </Style>
            <Style TargetType="TextBox" BasedOn="{StaticResource TextBox}"/>
        </Grid.Resources>

        <TextBlock Text="Value A"/>
        <TextBox Text="{Binding ValueA, UpdateSourceTrigger=PropertyChanged}"
                 Style="{StaticResource TextBoxA}"/>

        <TextBlock Text="Value B" Grid.Row="1"/>
        <TextBox Text="{Binding ValueB, UpdateSourceTrigger=PropertyChanged}"
                 Style="{StaticResource TextBoxB}"
                 Grid.Row="1"/>

        <TextBlock Text="Value C" Grid.Row="2"/>
        <TextBox Text="{Binding ValueC}"
                 IsReadOnly="True"
                 Grid.Row="2"/>

        <TextBlock Text="Value D" Grid.Row="3"/>
        <TextBox Text="{Binding ValueD}"
                 IsReadOnly="True"
                 Grid.Row="3"/>


    </Grid>
</Window>

When your mouse hovers over a textbox, the textbox background will change color, and when you enter a numeric value in either of the first 2 textboxes, the values in the last 2 will auto calculate. The key is Data Binding. Take your time and learn how this works from the links provided above.