Gluttony

Algebra Level 1

There is a circular cake, which you are told to cut into 7 or 9 equal pieces.

If you cut it into 7 equal pieces, then you're allowed to take 4 of them.
If you cut it into 9 equal pieces, then you're allowed to take all but 4 of them.

If you want to maximize the amount that you take, should you cut the cake into 7 or 9 equal pieces?