Let's assume that both machines start with a full capacity of ice cream.
Let x represent the number of days that have passed.
The amount of vanilla ice cream left after x days is 180 - 20x.
The amount of chocolate ice cream left after x days is 140 - 16x.
To find when the two machines will have the same amount of ice cream left, we set up the following equation:
180 - 20x = 140 - 16x
Simplifying the equation, we get:
-20x + 16x = 140 - 180
-4x = -40
x = (-40)/(-4)
x = 10
Therefore, the two machines will have the same amount of ice cream left after 10 days.