Question 1095256
This solution is being done with just one variable:
x, volume of the 30% alcohol
18-x, volume of the 60% alcohol


{{{30x+60(18-x)=50*18}}}, to account for pure alcohol

-

{{{3x+6(18-x)=5*18}}}
{{{x+2(18-x)=5*6}}}
{{{x+36-2x=30}}}
{{{-x=-6}}}
{{{x=6}}}



6 liters of 30% alcohol
12 liters of 60% alcohol