How to convert currency format label to double for calculation purpose

Question

I have a label (lblAmountTendered) which contains Currency String in it. I would like to convert it into double to perform some calculation. However, it shown an Error Message: Input string was not in a correct format in the first statement.

Here is my code:

double balance = double.Parse(amount) - double.Parse(lblAmountTendered.Text.ToString());
lblBalanceDue.Text = balance.ToString("c2",CultureInfo.CreateSpecificCulture("en-MY"));

For Example:

lblAmountTendered = RM 15
I want to retrieve the value of it (15) for calculation.

Looking forward for the solution. I appreciate for your help! :)

PROBLEM SOLVED
lblAmountTendered.Text.ToString(). Remove(0,3)

Remove(0,3) helps us to remove 'RM' from 'RM 15', so we can convert it to double or float easily as shown in below:

float.Parse (lblAmountTendered.Text.ToString(). Remove(0, 3) )

Answer 1

Here you first need to retrieve the numeric value from a string using below regex:

string resultNum = Regex.Match(lblAmountTendered.Text, @"\d+").Value; 

and then use resultNum in your code like-

double balance = double.Parse(amount.ToString()) - double.Parse(resultNum);
lblBalanceDue.Text = balance.ToString("c2",CultureInfo.CreateSpecificCulture("en-MY"));