Ok, let’s take it step by step.
Let x = number of gallons of 70% solution
100 = number of gallons of 25% solution
Then x + 100 = number of gallons of a 60% solution.
0.70x + 0.25(100) = 0.60(x + 100)
0.70x + 25 = 0.60x + 60
0.10x = 35
x = 350 gal
So, you can mix 350 gal of a 70% solution with 100 gal of a 25% solution to get 450 gallons of a 60% antifreeze solution.
