Question

For a promotion, a store offers to pay the sales taxes on any item

Answer 1

You buy an item for $100 with 15% added tax. So we find 15% of 100:
100 • 0.15 = 15

(A quick math here, and percentage of 100 will always be the same number of the percentage, for example 32% of 100 will be 32.)

100 + 15 = 115

a) the true sale price of the item is $115 (with tax included)

b) you are buying a $15 tax (for the item)

(I hope these are correct, the questions are really vague)