formula for deriving taxable amount from total amount.

hi,

can anyone help on this ?

I have a invoice with GST rates of 5%, 12%, 18%, 28% columns.
I want the sum of taxable value i.e. amount before GST.
5% amount before GST in G26 cell,
12% amount before GST in G27 cell,
18% amount before GST in G28 cell,
28% amount before GST in G29 cell,


thanks in advance.