Math homework quadratic formula

Question

I am having a really hard time solving this equation.

The area of a rectangle is 40. The length is x and the width x+4. Solve for x.

Answer 1

length x width = area

length = x

width = x + 4

area = 40

x(x + 4) = 40

x² + 4x = 40

x² + 4x - 40 = 0

a = 1

b = 4

c = -40

Plug these values into the quadratic formula and get x. Note that x must be positive, so only one of your two solutions will be correct.