Martin finds a shirt for $20 the sign says it is 10% off the original price. martin must also pay 8.5% sales tax. what is the cost of the shirt before and after the sales tax?

Z= (10/100) * 20
z=2    therefore 10% is $2
you do 20+2 because it was 10% off so you add the 10% to get the original price.
original price= $22
turn 8.5 into decimal 
0.85 * 22 = 18.70 therefore there is a $18.70 tax.
You add 22+18.70 to find price after tax
after tax= $40.70
before tax= $22
(i really don't know if this is correct but there is a 95% chance this is right and a 5% chance it is wrong and if it is please forgive me)