Your family plans to take a vacation this summer. For the cost of the vacation to be manageable, you determine that it will be in the best interest of your family to share a vacation home with other families. The cost c (in dollars) per family of the vacation home is inversely proportional to the number t of families sharing the house. Your family wants the cost of the house per family to be $600. Currently, with three families (including your family), the vacation home rental cost is $1000 per family. How many more families have to join to get the vacation home to be manageable for your family?