A rectangular piece of sheet metal is 4 ft longer than it is wide. The area of the piece of sheet metal is 45 ft2. Find its length and width.
width --- x
length ---- x+4
x(x+4) = 45
x^2 + 4x - 45 = 0
factor it, the factors are obvious.
make sure to reject the negative answer, since a negative width makes no sense