Answer
The dimensions of the lot are 100ft x 80ft
Work Step by Step
l= length (ft)
w = width (ft)
Perimeter: 360 ft
2l + 2w = 360
Fencing is 20 per ft for the length of the fence (20l)
Fencing is 8 per ft for the width of the fence (8 $\times$ 2w)