Question

find the surface area of the rectangular prism that is 16 inches long, 12 inches wide, and 5 inches in length

Answer 1

Surface Area of a closed rectangular Prism equals to twice the area of the base plus the perimeter of the base multiplied by the height.

In your question:
 
Area of the base = (16)(12) = 192
 
Twice the Area of the base = 2(192) = 384
 
Perimeter of the base = 2(16) + 2(12) = 56
 
Surface Area = Twice the Area of the base + the Perimeter of the base x height
 
S.A. = 384 + 56 x 5

The surface area is 664 in². Hope that helps.
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Answer 2

960 square unit

length x width x height