To solve this problem, we need to know the formula of the surface area of a triangular prism. The formula is: A = 2
+ (a+b+c) * h
Now we can substitute values and solve
A = 2(0.5 * 4 * 3) + (3+4+5) * 20
A = 12 + 240
A = 252
That means that the answer to this question is 252 square feet.