Hi,
The perimeter of a rectangle is 36 inches. 
If the length is 4 inches longer than the width, find the dimensions

Let x represent the width, then (x+4) is the length
Question states*****
 36 = 2(x+4) + 2x
Solving for x
2x + 8 + 2x = 36
4x = 28
x = 7in, the width.  The length is 11in  (x+4)
CHECKING our Answer***
 22in + 14in = 36in