How do I use the data entered in the textbox in my loadmonthlypayments() and monthlypayment initializemyobject() method?

public class MonthlyPayment
    {
        public int Luna { get; set; }
        public double SoldInitial { get; set; }
        public double PlataLunara { get; set; }
        public double Dobanda { get; set; }
        public double Principal { get; set; }
        public double Asigurare { get; set; }
        public double Comision { get; set; }
        public double TotalLunar { get; set; }
        public double SoldCredit { get; set; }
        
    }

public class CreditDataContext {
  public List<MonthlyPayment> MonthlyPayments { get; set; }

  public void LoadMonthlyPayments() {
    MonthlyPayments = new List<MonthlyPayment>();
    MonthlyPayment payment = null;
    payment = new MonthlyPayment() {
      Luna = 0,
      SoldInitial = 0,
      PlataLunara = 0,
      Dobanda = 0,
      Principal = 0,
      Asigurare = 0,
      Comision = 200,
      TotalLunar = 200,
      SoldCredit = 10000
    };

    MonthlyPayments.Add(payment);

    for (int i = 1; i <= 12; i++) {
      MonthlyPayments.Add(InitializeMyObject(i, MonthlyPayments[i - 1]));
    }
  }

  public MonthlyPayment InitializeMyObject(int i, MonthlyPayment lastMonth) {
    MonthlyPayment x = new MonthlyPayment();
    x.Luna = i;
    x.SoldInitial = Math.Round(lastMonth.SoldCredit, 2);
    double s = 10000;
    double a = 0.10 / 100;
    double c = (0.5 / 12) / 100;;
    double d = (9.75 / 100) / 12;
    x.Dobanda = Math.Round(d * lastMonth.SoldCredit, 2);
    double v = 1 + d;
    x.PlataLunara = Math.Round((s * d) / (1 - Math.Pow(v, -12)), 2);
    x.Principal = Math.Round(x.PlataLunara - x.Dobanda, 2);
    x.Asigurare = Math.Round(a * lastMonth.SoldCredit, 2);
    x.Comision = Math.Round(c * s, 2);
    x.TotalLunar = Math.Round(x.Comision + x.Asigurare + x.PlataLunara, 2);
    x.SoldCredit = Math.Round(lastMonth.SoldCredit - x.Principal, 2);
    return x;
  }

<pre><TextBox x:Name="textBoxValoareCredit" Width="100" Height="30" Margin="10" VerticalAlignment="Bottom"/>
//textbox for a
//textbox foc c
.....

double SoldInitial, Dobanda,ComisionAnaliza,Asigurare,Comision;
           SoldInitial= float.Parse(textBoxValoareCredit.Text);
            Dobanda = float.Parse(textBoxDobanda.Text);
            ComisionAnaliza = float.Parse(textBoxComisionAnaliza.Text);
            Asigurare = float.Parse(textBoxAsigurare.Text);
            Comision = float.Parse(textBoxComisionLunar.Text);