Write a cost function C(x) for the total cost?

Jon is planning to sell candy apples at the county fair, The cost to rent the boot his $50.00 and he estimates the cost for supplies will be .25 per apple. He plans to sell the apples for $2.50 each

Write a cost function C(x) for the total cost?
c(x) = -2.25a + 50b (apples and booth)





or





c(x) = .25p + 50b - 2.5s (apples purchased, booth, and apples sold)





This is cost to him.