Question 708649
Taking the format of quantity*concentration,

{{{x*70+70*25}}} = actual antifreeze substance



{{{(x*70+70*25)/V=60}}},  the desired concentration is 60%. Volume V is still unknown.



Known also is that this starts with 70 gallons of one of the antifreeze solutions, so,
x+70=V, which we might have used already in setting up the "60%" equation.


Let's do that, already:
{{{(x*70+70*25)/(x+70)=60}}}
THAT is what we want to solve; solve for x.