Step-by-step explanation:
Let x be the width of the parking lot. Then (x + 10) is the length of the parking lot.
x(x + 10) = 600
x^2 + 10x = 600
x^2 + 10x - 600 = 0
(x+30)(x-20) = 0
x = 20 or x = -30 (rejected as x must be positive)
Hence the length is 30 yards and the width is 20 yards.