The dimension of front face is l=4 ft and b=12 ft.
Determine the area of each front face of prism.

The dimension of top face is l=4 ft and b=7 ft.
Determine the area of each top face.

The dimension of side face is l=7 ft abd b=12 ft.
Determine the area of each side face.

Determine the total surface area of prism.

So total surface area of prism is 320 square feet.