The tax and the total per night is calculated with $120 * 118%. You then will get $120*1.18, which is, $141.6. To get the tax alone, you can multiply $120 to 18%, and get $21.6.
Remember that percentages are basically a fraction over 100. (Ex. 18% is 18/100. You can simplify it to 0.18)
It will cost $21.6 in tax each night alone, but will cost $141.6 in total.
