4. Firm's Costs

Your cousin Vinnie owns a painting company with fixed costs of $250 and the following schedule for variable costs:

Quantity (Houses Painted per Month)	Variable Cost (Dollars)	Average Fixed Cost (Dollars)	Average Variable Cost (Dollars)	Average Total Cost (Dollars)
1	8
2	20
3	50
4	160
5	320
6	500
7	720

The efficient scale is ___________ houses.