Hi Amanda,
Profit = Revenue - Cost
Profit = 625q - q2 - 50 - 6q
Profit = 619q - q2 -50
Now the Profit will have a maximum when the derivative is equal to zero
0 =619 -2q
619 = 2q
q = 309.5
the profit will be a maximum at 309 and 310
The maximum profit will be 95740
Hope this helps