A manufacturer produces 1,000 basketballs each day, which it sells to customers for $30 each. All costs associated with production and sales total $10,000; however, if the manufacturer were to produce one additional basketball per day, total costs would increase to $10,100. From these amounts, we can tell that:________

a. the firm has negative profit.
b. marginal cost equals $100.
c. marginal cost equals $150.
d. marginal cost equals marginal revenue.