step 1) Multiply your subtotal by the applicable tax rate and enter the tax charged below your subtotal. So, if your subtotal is $16.40 and you need to apply sales tax at 9 percent, multiply $16.40 by 0.09 to arrive at $1.48. Add your subtotal to the tax your're charging to arrive at the total amount due.
step 2) If you want to leave a 20% tip, multiply the cost by 0.20 to get the tip amount or multiply the cost by 1.20 to get the total including tip.
step 3) if you haven't already add the amounts you got for the tax and tip to the subtotal $16.40 and you will get the answer: $21.46
