Answer
$a$.
$P(x)=-0.05x^{3}+0.8x^{2}+155x-500$
$b.$
$P(15)={{\$}} 1836.25$
$\mathrm{c}$.
The profit on the sale of 1500 cell phones is ${{\$}} 1836.25$
Work Step by Step
$a$.
$P(x)=R(x)-C(x)$
$=(-1.2x^{2}+220x)-(0.05x^{3}-2x^{2}+65x+500)$
$=-1.2x^{2}+220x-0.05x^{3}+2x^{2}-65x-500$
$=-0.05x^{3}+0.8x^{2}+155x-500$
$b.$
Substitute x=15 into the result of a.
$P(15)=-0.05(15)^{3}+0.8(15)^{2}+155(15)-500$
$=-168.75+180+2325-500$
$={{\$}} 1836.25$
$\mathrm{c}$.
The profit on the sale of 15 hundred cell phones is ${{\$}} 1836.25$
