Room prices are regularly $100, but for each additional room rented by a group, the price is reduced by $3 for each room. For example, 1 room costs $100, 2 rooms cost 2 * $97= $194, and so on. 

(a) Write a quadratic function C that gives the total cost of renting x rooms. 

(b) What is the total cost of renting 6 rooms? 

(c) How many rooms are rented if the cost is $730? 

(d) What number of rooms rented gives the greatest cost?