Multiple Formulas? Linking conditions...

Hi guys,

I'm looking for a formula that links different conditions together.

For example, I'm entering the formula into G9 and I want the formula to be if G7 is equal or greater to G16 then the answer should be 30, if not then the answer is 0.

Simple enough I know this is my formula to use "=IF(G7>=G16,30,0)" but I want it to look past that.

Basically I want it to say if G7 is equal or greater to G16 then the answer is 30, if not it's 0 BUT if G7 is equal to greater than G17 my answer is 60 BUT if my answer is equal to or greater than G18 my answer is 120.

G17 will always be a larger number than G16, and G18 will always be a larger number than G17.

Does that make any sense at all?

Thanks,
V