Joe's plumbing company estimates that its weekly profit, P, in hundreds of dollars, can be approximated by the formula P=-4x 24x 3 where x is the number of units produced per week, in thousands.
How many units should the company produce per week to earn the maximum profit?
Find the maximum weekly profit.

Find the derivative of the profit formula and then set it to zero. Solve for x and that is the units produced to give maximum profit.

If you don't know how to differentiate, then find the optimum point of the curve by completing the square. (or other method you might know to get the vertex)