Width = W
Length = L = 5W - 57
Perimeter = P = 2W + 2L = 210
2W + 2L = 210
2W + 2(5W - 57) = 210
2W + 10W - 114 = 210
12W - 114 = 210
12W = 324
W = 27
2W + 2L = 210
2(27) + 2L = 210
54 + 2L = 210
2L = 156
L = 78
Answer: The length is 78 feet and the width is 27 feet.