30 dollars = your food bill at the restaurant
Now, you leave 20% for tip..
20% = .20
Then the sales tax charged for your bill is 6%
6% = .06
How much will you be paying in total?
=> 30 dollars * .06 = 1.8 - is the sales tax that will be added to your bill
=> 30 dollars + 1.8 dollars = 31.8 dollars.
then let's calculate the tip which is 20%
=> 31.8 * 0.20 = 6.36
31.8 + 6.36 = 38.16 dollars or approximately 83 dollars