Three enterprising, politically correct teenagers, Tom, Dick, and Susie, wash cars for spending money. They each have their own customers whose cars they wash once weekly. Although they are competitors they got together a few weeks ago and cooperatively leased a mobile car wash unit and agreed to split the rental fee proportionally among them based on their individual usage of the machine. The first week, Dick's share of the rent was six dollars and Tom used the machine three times. The following week each of the three added one more weekly customer and Susie paid seven dollars and twenty cents as her share. In the third week, they each once again added one client and Tom owed five dollars toward the rent. How much is the weekly lease payment on the machine?