19 is correct
20. The total sale is
.. total = (book price) + (tax rate)*(book price) . . . . math for adding tax
.. total = (book price)*(1 +(tax rate)) . . . . . . . . . . . . . factor out book price
.. total/(book price) = 1 +(tax rate) . . . . . . . . . . . . . . divide by book price
.. (total/(book price)) -1 = tax rate . . . . . . . . . . . . . . subtract 1
25.02/24 -1 = tax rate = 1.0425 -1 = .0425 = 4.25%
