The equation for profit is:
P(x) = R(x) - C(x) (profit = revenue - cost)
We have:
P(x) = 7x³ + 300x² + 900x - (3x³ + 450x²) = 4x³ - 150x² + 900x
This is a third degree polynomial, the leading coefficient is 7
There is no constant term. However P(x) can be factored as 2x(2x² - 75x + 450)
The company will break even when P(x) = 0
Obviously, the polynomial equals 0 when x = 0 (x represents the time in months)
Our focus is on 2x² - 75x + 450 = 0
We can use the Quadratic Formula to solve this.
The roots are x = 30 and x = 15/2 = 7.5
The company will break even after 7.5 months, and after 30 months
We have already factored P(x) above