So first you start with finding 30%, and you do this by entering into a calculator 30 divided by 100 and then times it to the original book price. So:
30 divided by 100 x 15.40 = $4.62
So $4.62 is 30%, meaning all you have to do is take the original price of $15.40 and add the $4.62, so:
$15.40+$4.62= $20.02
