Question 714001
x be the volume of the 60% alcohol to use, and y is volume of the 90% alcohol to use. 

{{{(60x+90y)/15=76}}} and {{{x+y=15}}}


{{{(4x+6y)/1=76}}}, when numerator and denominator each divided by 15.
Divide both sides by 2 and obtain {{{2x+3y=38}}}.


Solve this system for x and y:
{{{highlight(2x+3y=38)}}}
{{{highlight(x+y=15)}}}