Sam quits his job as an airline pilot and opens his own pilot training school. He was earning $40,000 as a pilot. He withdraws $10,000 from his savings where he was earning 6 percent interest and uses the money in his new business. He uses a building he owns as a hanger and could rent it out for $5,000 per year. He rents a computer for $1,200, buys office supplies for $500, rents an airplane for $6,000, pays $1,300 for fuel and maintenance, and hires one worker for $30,000. Sam's total revenue from pilot training classes equaled $90,400. Sam's implicit costs for this year are equal to:

a, $84,400
b, $39,000
c, $55,000
d, $45,600