Say width equals x.
Length = 3x - 4
Solve for x: 72 = 2(3x - 4) + 2x
72=6x-8+2x
80=8x
X=10
So width = 10
Length= 3(10) - 4 = 26
The radius is 2 yards...
Formula for circumference is

so divide your circumference by 3.14 or pi and you get 4 the square root of 4 is 2.
Hope this helps!