How to solve a stated problem

[Motherof8]

THe area of a rectangle is 144 ft. It is 7 feet longer than it is wide. What is the width of the rectangle?

I know that the area of a rectangle = length x width. I said the width was x and the length was x + 7. I wrote this equation: x(x + 7) = 144. x squared + 7x - 144 = 0. How do you work this quadratic equation out?

I can't think of any number that one could multiply to get 144 that when subtracted, = 7. 12 x 12 =144 and 6 x 24 = 144, but neither numbers when added or subtracted = 7.

[Luke53]

x^2+7x-144=0
x=9 or x=-16
x=9, since a rectangle has no negative lenght.
9*16=144