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?
The classes in the pack cost $7.5 each because 75 / 10 = 
<gadget id="calculator">75/10</gadget>
<output>15/2 = around 7.5</output>
7.5.
An additional class costs $10 because 7.5 x (1 +(1/3)) = 
<gadget id="calculator">7.5*(1+(1/3))</gadget>
<output>10</output>
10.
She buys 3 extra classes because 13 - 10 = 
<gadget id="calculator">13-10</gadget>
<output>3</output>
3.
Her three additional classes cost $30 because 3 x 10 = 
<gadget id="calculator">3*10</gadget>
<output>30</output>
30.
Her total cost is $105 because 75 + 30 = 
<gadget id="calculator">75+30</gadget>
<output>105</output>
105.

<result>105</result>