I would be very grateful if someone could help me with the following formula
problem.

I would like cell H to calculate in a certain way when there is a value in
cell G and also cell H to calculate in a certain way when there is a value in
cell F.
when there is a value in F i would like it to calculate the following
formula:
PI()*E4/(6.5*F4)
when there is a value in cell G i would like it to do the following formula:
PI()*E4/G4
I would like it set up so that it will not calculate if there is a value in
F and G.