Given:
Filled with 12 liter
Butterfat = 4%
Mixture butterfat = 2%
Find-:
How much 1% milk is added
Explanation-:
Let

The total amount is:

The amount of butterfat equation is:

Solve for "x"

Then the value of "x" is:

So, x=24 liters
24 liters of 1% milk required.