Answer:
The answer is 20
Explanation:
There's two ways in which you can do this. The first one, and the simpliest one is finding the derivative of the equation P(x). After finding the derivative, set the dy/dx to be zero (so set the derivative to be zero). Then solve for x. This should give you the point at which there's no increase or decrease in the value of P, thus meaning the point at which its the maximum.
The second method is simply ploting a graph and finding the highest point.