The perimeter is twice the sum of the length and width, but the width is the length less 5 inches. Let "L" represent the length.

P = 2*(L + (L - 5 in)) (your equation)

50 in = 2(2L - 5 in)

25 in = 2L - 5 in

30 in = 2L

30/2 in = L = length = 15 in.

L - 5 in = (15 - 5) in = 10 in = width

P = 2*(L + (L - 5 in)) (your equation)

50 in = 2(2L - 5 in)

25 in = 2L - 5 in

30 in = 2L

30/2 in = L = length = 15 in.

L - 5 in = (15 - 5) in = 10 in = width