How do i tell sales tax of 2.50 how much is the total

You can do is/of = %/100
you don't know what the sales tax is yet so the "is" is x and you want to know how much out of 2.50 so that is "of" sales tax is 6% so that goes over 100. the final equation is
x/2.50=6/100 and you have to cross multiply and divide. you multiply 6 and 2.50 and then divide by 100 which is .15. the sales tax is .15 and you add that to 2.50 so the total after adding the sales tax is 2.65.