Question

A carpenter is building a bookcase. The perimeter of the top is 108 in. If the width is 8 in., what is the length of the shelf?

Answer 1

46 inches

Perimeter = 2 x length + 2 x width.
Width = 16 (2x 8)
Subtract that from the perimeter (108) to get 92. 
92 = 2 x length
Divide 92 by 2 to get 46 = length. 

Answer 2

The length of the shelf would be 46" (inches)