Answer:
20 quarts of 6% butterfat milk and 40 quarts of 3% butterfat milk is used to make 60 quarts of 4% butterfat milk.
Explanation:
We are given the following in the question:
Let x quarts of 6% butterfat milk be used and y quarts of 3% butterfat milk be used to make 60 quarts of 4% butterfat milk.
Thus, we can write the equation:
![6\%* x + 3\%* y = 4\%* 60\\6x + 3y = 240](https://img.qammunity.org/2021/formulas/mathematics/middle-school/x25w1gslt7w57vx8icruu6ys3wx6jf2dx9.png)
Total amount of 3% butterfat milk = 60
Thus, we can write the equation:
![x+y = 60](https://img.qammunity.org/2021/formulas/mathematics/middle-school/xhzdhnkjarlexorhw17d43t2fp87qugdej.png)
Solving the two equation, we get,
![6x + 3y-(3x+3y) = 240 - 3(60)\\3x = 240-180\\3x = 60\\x = 20\\y = 60-20 = 40](https://img.qammunity.org/2021/formulas/mathematics/middle-school/tausqt6uzkdajqii21wy2pekfm5gun97w0.png)
Thus, 20 quarts of 6% butterfat milk and 40 quarts of 3% butterfat milk is used to make 60 quarts of 4% butterfat milk.