Answer: 338.5 mm²
Explanation:
There are 3 rectangles for the lateral surface area
LA=Ph lateral surface area is the are around which is found Permiter*height
LA=(7.5+10.5+11)9.5=275.5
Total area = LA + 2B B is the area of the base 1/2 bh
A=275.5+2(1/2)(10.5)(6)
=338.5 mm²