We know:
Profit = Revenue - Cost
When Revenue is equal to Cost, we have the break-even point.
Let's equate revenue and cost:
[tex]\begin{gathered} R=C \\ x^2-15=7x+11 \end{gathered}[/tex]To find the value of x, we can take all terms to LHS (Left-Hand-Side) and use the quadratic formula. The process of finding x is shown below:
[tex]\begin{gathered} x^2-15=7x+11 \\ x^2-15-7x-11=0 \\ x^2-7x-26=0 \\ u\sin g\text{ quadratic formula,} \\ x=-2.7,9.7 \end{gathered}[/tex]We can't have a negative value, so we disregard x = -2.7
What we have is
x = 9.7
So,
For 10 units (and above) sold, we will have a profit.
For 9 units (and below) sold, we will incur a loss.