How many different criteria do you have? If it is only a few then you
could use a nested IF function, such as:
=IF(I26=1,G6*J29,IF(I26=2,G6*K29,IF(I26=3,G6*L29,0))) etc
If you have several more conditions then it would be better to use some
kind of LOOKUP formula, where you can get the %age values from a table,
as you can only have up to 7 nested IFs.
Hope this helps.
Pete