The objective function is

Profit = Revenue Cost
= pq 8q

= 360/p^0.5 2,880/p^1.5.

The only critical point accours when p = 24, and this is seen to be an absolute maximum. (Graph the function in the window 0 p 55, 0 y 50 to see why.)

Thus, the bookstrore should charge $24 per pair of shorts to maximize profit.