Find how many quarts of 4% butterfat milk and 1% butterfat milk should be mixed to yield 45 quarts of 2% butterfat milk. The mixture should contain quarts of the 4% butterfat milk.

15

Step-by-step explanation:

30 quarts of 1 percent combined with 15 quarts of 4 percent would equal 45 quarts of 2%

step-by-step explanation:

the ratio of red paint to blue paint is always 9/7. that means that, whatever x's value, (4x+12)/(4x-4) has that same ratio. so, set up an equation and cross-multiply to solve for x:

9/7 = (4x+12)/(4x-4)

9(4x-4) = 7(4x+12)

36x - 36 = 28x + 84

8x - 36 = 84

8x = 120

x = 15