answer: $18.19
step by step explanation:
first you must find the amount of money that lins father gets off on the coupon by using the equation 20•0.15=3 meaning that lin’s father gets 3 dollars off
next you find the pre-tax total which in this case would be by using the equation 20-3=17 so the pre-tax total is 17 dollars
then you find the percentage of the tax that you have to add on to the pre-tax total which would be using the equation 17•0.07 and that equals 1.19 dollars in tax
finally, you add the pre-tax total with the sales tax by adding the two (17+1.19) to get a total of 18.19 dollars or $18.18