What is the surface area of a triangular prism

To work out the surface area of a triangular prism:
Base: l x w
= 4 x 7
= 28 feet 

Top: l x w
= 5 x 7 
= 35 feet

Two sides: 1/2 x b x h 
= 1/2 x 4 x 3
= 6 + 6 (for the other side)
= 12 feet

Left side: l x w
= 3 x 7
= 21

Add all of them up:
= 28 + 35 + 12 + 21
= 96 square feet