The Stick-em-Quick Inoculations Center (SQIC) provides early childhood checkups and vaccinations for children in the South Bronx. It pays annual rent of $25,000 and has a permanent staff consisting of...

The Stick-em-Quick Inoculations Center (SQIC) provides early childhood checkups and vaccinations for children in the South Bronx. It pays annual rent of $25,000 and has a permanent staff consisting of a nurse practitioner and an administrative assistant, who are paid $125,000 in total per year. SQIC hires doctors on a per diem basis to provide exams and uses $15 worth of supplies for each exam, not including vaccines. Inoculation appointments are scheduled in advance, and SQIC needs one per diem doctor for every 100 children it has scheduled on any given day. It also spends $7.50 per child for the vaccines used in its inoculations program. Which of Stick-em’s expenses are

a. fixed,

b. step-fixed or semi-variable costs, and

c. variable?