Explanation:
Profit is maximized at the production point of four tops. The disparity in net income and net expenditure is highest in this amount.
Another way of talking about this is to note that for the first 4 shirts that Gilberto makes, the marginal cost (MC) of making each shirt is smaller than the total revenue (MR) it generates from selling the shirt.
Beyond just the third shirt he makes per hour, the total cost of making the shirt is higher than the amount Gilberto receives; thus, opting to manufacture more than 4 shirts decreases Darnell's benefit.