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