Answer:
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.