Final answer:
The total cost of the dinner including a 20% tip will be $78.
Step-by-step explanation:
To find the total cost of the dinner, we need to add the cost of the meal and the tip. First, let's calculate the tip amount. The bill for the dinner is $65. To find the 20% tip, we multiply $65 by 0.20. The tip amount is $13.
Now, to find the total cost of the dinner including the tip, we add the tip amount to the bill. The total cost is $65 + $13 = $78.