Comparing to results in method C# wpf

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C#

WPF

I have a project that is a vending machine:
But i have a problem comparing code:

There a buttons for choosing the drink and it has the prices to a label if clicked on the drink:

example code drink:

private void btnCola_Click(object sender, RoutedEventArgs e)
{
    Drank d;
    d = new Drank();
    double cola = d.coladrank();
    lblSortDrink.Content = cola;
    groupBox2.IsEnabled = true;
}

(Drank is sort drink)

i made class of this

partial class Drank
{
    public int cola;
    public int water;
    public int koffie;
    public int soep;

    public double coladrank()
    { 
        double cola = 1.00;
        return cola;
    }
}

The coin button become enable if clicked and stop when there is enough money. example code:

private void btnTwo_Click(object sender, RoutedEventArgs e)
{
    Geld g;
    g = new Geld();
    double tweeEuro = g.tweeEurogeld();
            
    if (Convert.ToDouble(lblSortDrink.Content) > (Convert.ToDouble((lblInsertedCoins.Content))))
    {
        result += tweeEuro;
        lblInsertedCoins.Content = result;
    }
    else
    {
        groupbox1.IsEnable = false;
    }
}

again i made a class of the coins:

partial class Geld
{
    public int tweeEuro;
    public int eenEuro;
    public int vijtigCent;
    public int twintigCent;
    public int tienCent;
    public int vijfCent;

    public double tweeEurogeld()
    {
        double tweeEuro = 2.00;
        return tweeEuro;
    }
}

now i cant seem to compare or do anything with the results?
and the groupbox1 is a click to many bacause if the price is the same or bigger you can still click the button do'h the coins dont add.