I have this assignment to do in my economics class and the first question has stumped me, just looking for some help. the question is as follows...

A manager hired an economist to evaluate the benfits and costs of increasing the number of square feet (S) of inventory space. The result of the study are as follows:

B(S)=4000-S^2
C(S)=S^2

Your assistant informs you that marignal benefits are MB=4000-2S and marginal costs are MC=S2

How many square feet should be added to max the net benefits?

Thanks!