$8.40 is the amount to be subtracted from the $42.00. If you multiply 20% (.20) by $42.00 you get $8.40. To get your final price subtract $8.40 from $42.00 to get you final answer. I hope that helps.
In order to get that answer you have to convert 20% to 0.2. Then you multiply $42 by 0.2. Once you multiply you will get 8.40. You will then subtract that from $42.00 to get $33.60
