The average cost per seat on the 50-passenger Floating-On-Air Bus company's trip from Kansas City to St. Louis, on which no refreshments are served, is $45. In advance of a particular trip, three seats remain unsold. The bus company could increase its profit only if it a. charged any ticket price above $0 for the three remaining seats. b. charged at least $15 for each of the three remaining seats. c. charged at least $45 for each of the three remaining seats. d. paid three people to occupy the three remaining seats.