Geometry Involving Quadratic Equation

The length of a rectangular field is 5 meters more than its width. Its area is 300 square meters. How long is the field?

Usually whatever comes after "than" is what you let x equal
x = width
x + 5 = length

Area of a rectangle is length x width
x(x + 5) = 300
x2+ 5x = 300 {distributive property}
x2+ 5x - 300 = 0 {subtract 300 from both sides}
(x + 20)(x - 15) = 0 {factor into 2 binomials}
x + 20 = 0 or x - 15 = 0 {set each factor equal to 0}
x = -20 or x = 15 {width cannot be negative}
x = 15 width
x + 5 = 20 length

- Algebra House