A senior citizen gets a part-time job at a fast-food restaurant. She earns $8 per hour for each hour she works, and she works exactly 25 hours per week. Thus, her total pretax weekly income is $200. Her total income tax assessment each week is $40, but she has determined that she is assessed $3 in taxes for the final hour she works each week.
a. What is this person's average tax rate each week?
b. What is the marginal tax rate for the last hour she works each week?