A company that manufactures radios first pays a start-up cost, and

then spends a certain amount of money to manufacture each radio.

If the cost of manufacturing r radios is given by the function

c(r) = 5.25r + 125, then the value 5.25 best represents

(1) the start-up cost

(2) the profit earned from the sale of one radio

(3) the amount spent to manufacture each radio

(4) the average number of radios manufactured