Three friends rented a car for a week and divided the cost equally. What was the total cost of renting the car?

1) If the three friends lad kept the car for a second week they could have obtained the two week rate, which was 1.5 times the cost of a one week rental.

2) If the fourth friend jioned the three friends and the cost had been divided equally among the four friends, the cost to each of the original three wold have been reduced by $15.