The surface area of a prism of heigh H and base of sides a, b, and c is:
A = PH + 2B
Where P = a + b + c is the perimeter of the base and B is its area.
We can see in the figure a prism of height H = 14 in, base sides of 10 in, 10 in, and 12 in. The height of the base is also given as h = 8 in.
Calculate the perimeter of the base:
P = 10 in + 10 in + 12 in = 32 in
The area of the base is:

Calculate the surface area:

The area is 544 square inches