Answer: The break-even point is x = 15
Explanation:
We have the equations:
c(x) = 10*x
r(x) = 210 - 4*x
I suppose that c(x) is the cost equation, and r(x) is the revenue equation.
"break-even" means that you don't lose nor win anything, then the difference between the revenue and the cost is 0.
Then we need to solve:
r(x) - c(x) = 0
(210 - 4*x) - (10*x) = 0
210 - 4*x - 10*x = 0
210 - 14*x = 0
210 = 14*x
210/14 = x
15
This means that for x = 15, you break even.