There is a sales tax of $15 on an item that costs $153 before tax. A second item costs $81.60 before

There is a sales tax of $15 on an item that costs $153 before tax. A second item costs $81.60 before tax. What is the sales tax on the second item?

We assume the goods are bought in the same store, so tax rates are the same:
Tax Rate = Tax Amount / Cost before tax
Tax Rate = 15/153
Tax Rate = 0.098 or 9.8%

Calculate sales tax on the second item
Sales Tax = Cost before Tax * Tax Rate
Sales Tax = 81.60 * 0.098
Sales Tax = 7.9968

We round to 2 decimals for dollars and cents and we get:
Sales Tax = $8.00