Arectangular parking lot has a perimeter of 820ft. the area of the parking lot measures 42000 ft2. what is the width of the parking lot.

2W + 2L = 820 
LW = 42,000 or L = 42,000/W 
substitute second equation into first equation: 
2W + 2(42,000/W) = 820 
2W + 84,000/W = 820 
2W^2/W + 84,000/W = 820W/W 
2W^2 - 820W + 84,000 = 0 
quadratic formula: 
W = [820 +/- SQR(672,400 - 4(2)(84,000))]/2(2) 
W = [820 +/- 20]/4 
W = 200, 210 
using second equation: 
L = 42,000/200, 42,000/210 = 210, 200 
The dimensions of the parking lot are 200ft by 210ft.