Kelly has saved $35 to take music classes. She must pay a registration fee of $15 and then an additional $5 for each class. Which equation will best help Kelly determine the number of classes she can afford?

15c - 5 = 35
15c - 5 = 35

5c - 15 = 35
5c - 15 = 35

5c + 15 = 35
5c + 15 = 35

15c + 5 = 35
15c + 5 = 35