I have a calculation that I need done only if a certain drop down field is selection (Yes/No option).

For example:

Drop down field - Is this a VAT customer?  Yes/No

If Yes:

Amount = 100

VAT Amount = Amount - (Amount / 1.19) 

Net Amount = Amount - (Amount - (Amount / 1.19)

If No

Amount = 100

VAT Amount = 0

Net Amount = Amount

Do you have any suggestions how I can reach this result?

Thank you