Assume that a firm's marginal revenue curve intersects the rising portion of the marginal cost curve at 100 units of output. At this output level, a profit-maximizing firm's total cost is $1,000. If the price of the product is $10 per unit, the firm will earn an economic profit of:

1. zero.

2. more than zero but less than $100.

3. more than $100.

4. $100.

5. $400.