How much cream that is 30% butterfat must be mixed with milk that is 3% butterfat to make 45 gal of cream that is 12% butterfat?

15 gallons

Step-by-step explanation:

If x is the gallons of 30% butterfat cream, and y is the gallons of 3% butterfat milk, then:

x + y = 45

0.30 x + 0.03 y = 0.12 (45)

Solve the system of equations with substitution or elimination. Using substitution:

0.30 x + 0.03 (45 - x) = 0.12 (45)

0.30 x + 1.35 - 0.03 x = 5.4

0.27 x = 4.05

x = 15

You need 15 gallons of 30% butterfat cream.