I would answer this but I am not sure
Elaborate what do the symbols stand for pmme if you need more help.
Are you looking for a rate? If not than I belive the answer is 21cents because if before the sales tax it was $3 and after it is $3.21, then the price increased by 21cents
10% of 12 is 1.2 and 10% of 20.1 is 2.01
