Estimating Profit An appliance manufacturer estimates that the profit $y$ (in dollars) generated by producing $x$ cook tops per month is given by the equation
$$
y=10 x+0.5 x^{2}-0.001 x^{3}-5000
$$
(a) Graph the equation.
(b) How many cooktops must be produced to begin generating a profit?
(c) For what range of values of $x$ is the company's profit greater than $\$ 15,000 ?$