The length of a rectangle is 8 feet more than its width the area of the rectangle is 84 square feet find its length and width.

X(x+8)=84
x²+8x=84
-84.    -84
x²+8x-84=0
(x+14)(x-6)=0
x+14=0 x-6=0
x=-14  x=6
^reject the -14 because you can't have a negative measurement

The width is 6 feet and the length is 14 feet (6+8=14)