10% off
original price=20
tax=8.5%
percent means parts out of 100
10%=10/100=0.10
10% of 20 then tax so
'of' in math means multiply
0.1 times 20=2
10% off
20-2=18
then tax is added
8.5%=0.085
8.5% of 18=0.085 times 18=1.53
that's tax to it's added on the 18
18+1.53=19.53
the shirt costs $19.53