In Exercises 13 and 14, determine whether the situation shows direct variation.
Explain your reasoning.
13. Bowling lane rental costs $3.00 per hour.
14. A family water park ticket costs $20 plus $5 for each tube.
15. In a rewards program, the number p of points a member earns varies directly
with the number d of dollars spent in the store. A member who spends $10 earns
5 points. Find the number of points a member earns for spending $80.