How to set up word problem/mixture problem.

Question

A mechanic has found that a car with a 12 quart radiator has 45% antifreeze mixture in the radiator. He has a 70% antifreeze solution. How much of the 45% solution would he have to replace with the 70% solution to get the radiator up to 60% antifreeze solution.

How do I set up this equation???

Answer 1

0.45(12 - x) + 0.70x = 0.60(12)

5.4 - 0.45x + 0.70x = 7.2

5.4 + 0.25x = 7.2

0.25x = 1.8

x = 7.2