11.4. Crazy Joe operates a canoe rental service on the Guadalupe River. He currently leases 15 canoes from a dealer in a nearby city at a cost of $10 per day. On weekends, when the water is high, he picks up the canoes and drives to a launching point on the river, where he rents canoes to white-water enthusiasts for $30 per day.

Lately, canoeists have complained about the unavailability of canoes, so Crazy Joe has recorded the demand for canoes and found the experience below for the past 20 days:

Daily demand 10 11 12 13 14 15 16 17 18 19 20 Frequency 1 1 2 2 2 3 3 2 2 1 1 Recommend an appropriate number of canoes to lease.