A suitable formula for the surface area of a rectangular prism is ...
A = 2(LW +H*(L +W))
Filling in the given information, we have
A = 2((9 ft)*(5 ft) +(7.5 ft)*(9 ft +5 ft))
A = 2(45 ft² +(7.5 ft)*(14 ft)) = 2(150 ft²)
The surface area of the rectangular prism is 300 ft².