Answer
(a) $A=-\frac{5}{2}x^2+375x$
(b) $28125ft^2$
Work Step by Step
(a) Assume the length of each pend divider is $x$, there are 5 such parts needs,
leaving the two other sides $750-5x$ in total length or $375-\frac{5x}{2}$ each.
The total area is $A=x(375-\frac{5x}{2})=-\frac{5}{2}x^2+375x$
(b) The maximum of the area happens when $x=\frac{375}{5}=75$ with $A=28125ft^2$