The profit P (in thousands of dollars) for a company spending an amount s (in thousands of dollars) on advertising is shown below.
P = [tex]\frac{-1}{10} s^{3} +3s^{2} +400[/tex]
(a) Find the amount of money the company should spend on advertising in order to yield a maximum profit.
s = _________ thousands of dollars

(b) The point of diminishing returns is the point at which the rate of growth of the profit function begins to decline. Find the point of diminishing returns.
s = __________ thousands of dollars