15 is just the tax. For example, if someone spends 2 hours getting tutored, the n that person pays 2 hours multiplied by 25, which is 50 bucks in total.
The options you gave are extremely confusing, but if you round 7.9 it is 8, and if you round $3.89 it is $4. Therefore, the best estimate would be 8•$4, or $32
