Tell me about time when you made a mistake how did you find it and what did you do to correct it

In the market for lock washers, a perfectly competitive market, the current equilibrium price is $5 per box. washer king, one of the many producers of washers, has a daily short-run total cost given by tc = 190 + 0.20q + 0.0025q2, where q measures boxes of washers. washer king's corresponding marginal cost is mc = 0.20 + 0.005q. how many boxes of washers should washer king produce per day to maximize profit?