Total of two different VAT in footer of Crystal Reports

Hello,

I have to show the total of two different VAT on the invoice.

My idea is to calculate the VAT of the invoicelines (INV1) of the two different VAT groups.

VAT Group A1

VAT Group A2

line     VAT group      VAT value

1          A1               5,00

2          A2               10,00

3          A1               3,00

4          A1               2,00

5          A2               4,00

So in the footer of the invoice i like to see:

Total of VAT Group A1     10,00

Total of VAT Group A2     14,00

I need the formula to get this result, something like:

sum ({INV1.VATSum}) where VAT Group = A1

I didn't find an example of an CR invoice or solution so far

Thanks,

Tim