If formula with multiple outcomes

Hi All

Apologies for this, but I don't seem the be able to find the answer but feel that it should be fairly obvious.

I need a formula that will calculate an If function but look at 2 different cells and subtract the amount in the cell that has a value (worksheet attached), either of the yellow boxes may have data in but could also be blank - I have managed to get it to work with one cell but not both with - =IF(ISBLANK(C2),A2,A2-C2). I essentially need the formula to subtract the amount that is in the yellow boxes.

Advise on if this is possible would be much appreciated

Thanks