To calculate final cost you need to add tax and tip. Because you tip on the food bill without tax, you just add these two.
72 0.2 = 14.4 -> tip
72 0.06 = 4.32 -> tax
72 + 14.4 + 4.32 = 90.72
So the total cost was $90.72
You can find that faster:
72 * 1.26 = 90.72
