The cost to rent skis at a local sporting goods store is $15 plus $20 per day. Which equation models the relationship between the total cost to rent, c, and the length of the rental in days, d?

The $15 is a one-time starting fee, and the $20 charge is added for each rental day. For d days, the daily charge is 20d, so the total cost is c = 20d + 15. Choice C, c = 20d + 15, models this relationship.

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