Perimeter, P = 2*(L + W)
Length, L = 14, Width = x
P = 2*(L + W)
38 = 2*(14 + x).
2*(14 + x) = 38, is the equation used to find x.
Let's go ahead and solve for x, though the question did not ask us to solve it.
14 + x = 38/2
14 + x = 19
x = 19 - 14
x = 5
Width is 5 inches.