Tommy rents office space for $12,000 per year. He uses the office to fill out tax return forms for his clients. He fills out 1,000 tax returns per year. If the owner of the building raises Tommy's rent to $13,000 per year, the marginal cost of filling out tax returns will

a. increase by $1

b. Increase by $100

c. increase by some amount that cannot be computed without the information

d. not change