Sales tax is 6%. how much tax would you pay on an item that normally costs $20, but is on sale at 15% off listed price. (show work xx)

If the item is on 15% sale, that means you would pay 85% (or 0.85) the price
$20 x 0.85 = $17
If you have to pay 6% sales tax, that would be 6% of $17. 
That is $17 x 0.06 which is 1.02
$1.02