Find the total cost of a spa treatment of $42 including 6% sales tax and 20% tip

Cost of the spa treatment = $42
Percentage of sales tax = 6%
Percentage of tips = 20%
Normally the tips amount is calculated before adding sales tax.
Then
Amount of tips given = (20/100) * 42
                                  = (1/5) * 42
                                  = 8.40 dollars
Amount of sales tax taken = (6/100) * 42
                                           = 252/100
                                           = 2.52 dollars
Then 
The total amount spent for spa treatment = (42 + 8.40 + 2.52) dollars
                                                                   = 52.92 dollars
So we can see that $52.92 has been spent in total for spa treatment and this amount includes a sales tax of $2.52 and a tip of $8.40.