We can use the data in Figure 11.2 below to find the profit-maximizing quantity. The owner should keep producing additional barrels so long as the revenue from producing an additional barrel exceeds the cost of producing an additional barrel. The first barrel of oil that the firm produces adds $50 to revenue and $4 to costs, so MR>MC, and by producing that barrel, the firm can add $46 to profit. On the second barrel, the marginal revenue is $50 and the marginal cost is $6, so producing that barrel adds $44 to profit. On the third barrel, the marginal revenue is ${ \} and the marginal cost is $ \}, so producing that barrel adds $ \} to profit. On the forth barrel, the marginal revenue is $ \} and the marginal cost is $1 \}, so producing that barrel adds $ \} to profit. Following through on this logic, we can see that each additional barrel of oil adds to profit up until the eighth barrel. If the firm produces the ninth barrel of oil, however, it adds $ \} to revenue but $1 \} to costs, so the firm will not want to produce the ninth barrel. Thus, the profit-maximizing quantity is 8