Hi Candisjhnsn,
To get the answer we need to add, subtract, and divide. So, for the first month we pay $115 cause $65 + $50 = $115. So, $850 - $115 = $735. Now, $735/$65 = 11.3076923077 but, you can't have .3076923077 of a class so, she will only have enough for 11 classes.
Hope This Helps!
Cupkake~