The dimensions are 120 ft by 180 ft.
Let L be the length. We know that L is 60 feet more than the width, or w+60=L.
We know that the perimeter is given by 2w+2L; in this case, we have 2w+2(w+60) = 600
Using the distributive property, we have
2w+2*w+2*60 = 600
2w+2w+120 = 600
Combining like terms,
4w+120=600
Subtract 120 from both sides:
4w+120-120 = 600-120
4w = 480
Divide both sides by 4:
4w/4 = 480/4
w=120
The width is 120; the length will be 120+60 = 180