I'm assuming you meant to type
So profit is sales-cost. Therefore,
To find the maximum, you must first differentiate giving you .
Then find the critical numbers by setting V'(x) to 0.
Quadratic formula gives you the critical values of x=98 and x=-94 but those aren't in the interval (0,9). So the maximum is when x is either 0 or 9. You can eliminate 0 because they would obviously make no profit if they didn't make a product. So plug x=9 into the profit equation.
The maximum profit is $251625