
Answer:
 $82.57
Step-by-step explanation:
The tip they leave is ...
 $78.64 × 0.20 = $15.73
The amount of the discount is ...
 $78.64 × 0.15 = $11.80
Then the total cost of the meal and tip is ...
 meal price - discount + tip
 $78.64 -11.80 +15.73 = $82.57