Question 415112
Let x gallons of 70% antifreeze mix with 100 gallons of 30% antifreeze we'll get (100+x) gallons of new solution
in 100 gallons of 30% antifreeze is {{{0.3*100=30}}} gallons of antifreeze
in x gallons of 70% antifreeze is 0.7x gallons
in (100+x) gallons of 60% antifreeze is 0.6(100+x) gallons 
Equation
{{{30+0.7x=0.6*(100+x)}}}
{{{30+0.7x=60+0.6x}}}
{{{0.1x=30}}}
{{{x=30/0.1}}}
{{{x=300}}} gallons of a 70% antifreeze solution must be mixed with 100 gallons of 30% antifreeze to get a mixture that is 60% antifreeze
Answer 300 gallons