When you're finding a percentage, you change the percent to a decimal. 20% is 0.20. Then you multiply the percent by the original amount. 22 x .20 = 4.40. So the discount is $4.40.
Now you subtract the discount from the original amount. 22 - 4.40 = 17.60.
Now multiply the tax times the current price. 17.60 x .09 = 1.584. You can't have part of a cent, so you round to 1.58. That the amount of tax you are paying.
Add the current price to the tax. 17.60 + 1.58 = 19.18. The amount paid will be $19.18.