To convert a percent to a decimal, you move the the decimal left two places to convert the percent to a decimal. For example, if you were to convert 14% to a decimal, you move the decimal left two places so that 14% converted to a decimal would look something like this: 0.14
The pree tax amount count as 100%, then there's the 7% tax and lastly the 20% tip. therefore, one would pay (100+20+7)% of $84.00. 127% of $84.00 (127/100) * $84.00 = $106.68