Since the cost function is

Since the revenue function is

Since the profit function is

Then we will subtract C from R

Add the like terms

Now, we will differentiate P(x) and equate the answer by 0 to find x maximum

Equate P' by 0 to find x

Subtract 88000 to both sides

Divide both sides by -8

The company should produce 11000 Phones to maximize the profit