Calculator project - equals operator help

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C#

Xamarin

I've been having difficulty fixing my equals function
Let's say I enter the operation 3 + 4, the result is 7 then 11 and so on. Working as intended same goes for multiplication.

However if I enter the operation 12 / 2 the result is 6 but when pressed again I receive 2 and pressing again gives 6, so obviously instead of calculating again I'm receiving the values of the next operation. This happens with subtraction as well.

Here's the following code:

private void BtnCommonOperation_Clicked(object sender, System.EventArgs e)
{
    var button = (Button)sender;
    isOperatorClicked = true;
    operatorName = button.Text;
    firstNumber = Convert.ToDecimal(CalcResult.Text);
}

public decimal Calculate(decimal firstNumber, decimal secondNumber)
{
    decimal result = 0;
    if (operatorName == "+")
    {
        return firstNumber + secondNumber;
    }
    else if (operatorName == "-")
    {
        return firstNumber - secondNumber;
    }
    else if (operatorName == "*")
    {
        return firstNumber * secondNumber;
    }
    else if (operatorName == "/")
    {
        return firstNumber / secondNumber;
    }
    return result;
}

private void BtnEquals_Clicked(object sender, System.EventArgs e)
{

    try
    {
        decimal secondNumber = Convert.ToDecimal(CalcResult.Text);
        string finalResult = Calculate(firstNumber, secondNumber).ToString("");
        CalcResult.Text = finalResult;

    }
    catch (Exception ex)
    {
        DisplayAlert("Error", ex.Message, "Ok");
    }
}

What I have tried:

I've tried inverting the order of firstNumber and secondNumber in the / and - operations and it seems to fix this issue, but will return me incorrect calculations of course for being out of order. If anyone can help me I'd be so happy.