Answer:
Given that Tom is making a punch that contains 80% cranberry juice and the rest ginger ale. The punch has 2 liters of ginger ale.
Part A:
Let the number of liters of cranberry juice be represented by = x
Then the total number of liters of the punch is given by

Now we have
(ginger ale is also added)
Solving this, we get


Further solving we get x = 2
So, the required equation with one variable is :

Part B.
From part A we have-

We will find x now, that is liters of cranberry added.
We have x =
= 8
Hence, there is 8 liters of cranberry juice in the punch.