To rent a bike, Max pays a flat rate of $5 plus an hourly rental fee. The graph shows the amount, C, in dollars, that Max pays based on the number of hours, t, that Max rents the bike. What is the rate of change in the cost to rent the bike with respect to the number of rental hours? $5 per hour

$2.50 per hour

$2 per hour

$7.50 per hour