You have the profit function
If you have a production level of 52, is it profitable to increase the production to 53 units?
To answer this question, you need to figure out whether the profit will increase or decrease after another unit is produced.
Start by finding from your profit function. That means you need to take the derivative of , and then insert :
As the answer is negative, the profit will decrease by 10 if you increase the production by one unit. You won’t want to increase production this time.