$6.4
so, if he gets 40% of a thing, that means he gets a reduced price.
to conduct sales tax, we need to move the decimal places 2 places to the left of the percent, so 40% becomes .40
then, multiply it to 8.50
that equals 3.4
3.4 is how much is taken away from him.
so, we subtract 3.4 from 8.50
that is 5.1. thats how much he gets from this haircut, but he gets a 1.30 tip
add 1.30 to 5.1
we get $6.4. thats how much he gets.