Let l = length
Let w = width
l = 4w (length is 4x width)
2l + 2w = 100 (perimeter is two lengths and two widths)
2(4w) + 2w = 100 (substitute)
8w + 2w = 100 (solve)
10w = 100
w = 10
l = 4(10) (plug in)
l = 40
The length of the rectangle is 40in and the width is 10in.
