What was the question for this implicit rationale, and corresponding answer?
The classes in the pack cost $7.5 each because 75 / 10 = 7.5. An additional class costs $10 because 7.5 x (1 + (1 / 3)) = 10. She buys 3 extra classes because 13 - 10 = 3. Her three additional classes cost $30 because 3 x 10 = 30. Her total cost is $105 because 75 + 30 = 105.
 The answer: 105
The question: Ruby is taking dance lessons. They cost $75 for 10 classes in one pack. She can add additional classes at the price of 1/3 more than the average price of a class on the lesson in the pack. if she takes 13 total classes, how much does she pay?