Check my answer? with precalc ?

the total cost (in dollars) of manufacturing scented candles is given by the function c(b) = 250+ 3b, where b is the number of candles manufactured. which function represents the average manufacturing cost, a, in terms od b?

a. a(b)= b/250+3b
b. a(b)= 250+3b/b
c. a(b)= (250+3b) * (b)
d. a(b)= 250+4b

i think it is either b or c. can someone tell me which it is and why?