If and Then help needed please

Hi All

I think that I need a piece of VB code that will enable me to do the following:

If then information in 'cell A' is equal to XX (text taken from a drop down list) then take the date in 'cell B' and add 20 working days to it, if it is equal to YY (again taken from the same drop down list) then take the date in 'cell B' and add 20 working days to it, but if it is equal to ZZ then take the date in 'cell B' and add 40 days to it (not working days).

I have found 'NETWORKDAYS' in the formulas and messed about with 'IF' statements etc, but don't seem to be able to make a fomula work, so think it will have to be code. As you can see I know exactly what I want the code to say, I just don't have enough experience to write it.

Big thanks to anyone who is able to offer any help or tips.

(I realise that no code is going to be able to accommodate for bank holidays!)