Question 1156055
<pre>
CONC.%     VOLUME LITERS     PURE ACID
  25           x              0.25x
  40           y              0.4y
  85          2y              1.7y          

  55          72            0.55*72=39.6
</pre>
You can have two equations.

{{{system(x+3y=72,0.25x+2.1y=39.6)}}}


They are equivalently 
{{{system(x+3y=72,x+8.4y=158.4)}}}


Their difference gives {{{5.4y=86.4}}}

{{{highlight_green(y=16)}}}
and you can easily evaluate the other acid solution volumes.