We know that L = 4W, and P = 2l + 2w, so 150 = 2L + 2w
So, 150 = 2*4w + 2w
150 = 8w + 2w
150 = 10w
w = 150/10
w=15
So, the Width of the Rectangle is 15 feet.
And if they asked you to find the length,
L = 4W
L = 4*15
L=60
so, the Length will be 60 feet.
Hope this Helps! :)