With the information provided, you have to add the result of multiplying the nine books for its price plus the remaining books for the price per book. To find the number of the remaining books you can substract the nine books from the total amount Mrs. Stewart purchased.
Cost=(9*4.95)+((15-9)*6.95)
Cost=44.55+41.7
Cost=86.25
According to this, the answer is that Mrs. Stewart paid $86.25 for all the books.
