At a restaurant, all tips are added together to be split among the employees at the end of a shift. The 4 waiters combined get 2/3 of the money, the manager receives 1/4 and the busboy receives the remainder. If 1 waiter and the busboy together receive $30, how much money was earned in tips for the entire shift?

a. $90

b. $96

c. $108

d. $120

e. $180