Answer:
Their cost would be $66.00
Explanation:
The way i do it is i take ten percent of the total. Which is 55. 10% of 55 is 5.5. And since the diners decide to leave a 20% you multiply 5.5 by two and get 11. So that is an $11.00 tip they left.
So next you would add the $11.00 tip to the $55.00 and you would get a total cost of $66.00.
The diners total cost after they leave a 20% tip would be $66.00