Business: maximizing profit. Custom Sport's total revenue and total costs, in dollars, from the sale of x logo t-shirts are given by
R(x) = 5x² + 12x + 150
C(x) = 5.4x² + 4x + 20
Find the number of t-shirts, x, that must be produced and sold in order to maximize profit.
a. 24
b. 10
c. 18
d. 9