the inventor charges $4.00 per unit, then her profit for producing and selling x units is given by the function P(x) = 2.25x - 7000

Question

(a) What is her profit if she sells 2000 units?
(b) What is per profit if she sells 5000 units?
(c) What is the break-even point for sales?

(a) Substitute 2000 for x in the equation for P(x). That will be the profit.
(b) ditto
(c) Set P(x) = 0 and solve for x. That is the number of sales needed to break even.