Question 1152235
Similar kind already answered

x, the 20% benzene
y, the 60% benzene

{{{system(20x+60y=40*4,x+y=4)}}}


E1:
{{{x+3y=2*4}}}
{{{x+3y=8}}}


System,  {{{system(x+3y=8,x+y=4)}}}


E1-E2,  {{{2y=4}}}
{{{highlight(y=2)}}}--------------------------two gallons of each of the benzene starting solutions.