Answer:
the bill before for the lunch before the tip was $13.75
Explanation:
Let bill before for the lunch before the tip was $x.
Now, it has been given that Mrs. chin paid a 20 percent tip on the bill for lunch.
Hence, the equation for the situation is

Now, solve the equation for x
Divide both sides by 0.20

Hence, the bill before for the lunch before the tip was $13.75