Question 792924
l = length = 3w -4
w = width 
P = perimeter = 360 yd = 2(l) + 2(w)

Plug in for l in the above equation, and solve for w (width) using algebra.

360 = 2(3w - 4) + 2w
360 = 6w - 8 + 2w
368 = 8w
46 = w

So, 

Using the value that we found for w, the width, we can now find the length.
l = 3w - 4
l = 3(46) - 4
l = 138 - 4
l = 134 yd