Let L be length and W be width.
L = 5 + W
So the perimeter is equal to 2L + 2W and that equals 50 feet.
So substitute L with 5 + W to get:
2(5+W) + 2W = 50
10 +2W + 2W = 50
10 + 4W = 50
4W = 40
W = 10
Which means:
L = 15
So the area is just LxW which is 15x10 = 150 feet squared
