Question 1184883
<pre>
CONCENTRATION%    VOL.      PURE(as decimal values, not "percent")
   25              x        0.25x
   40              y        0.40y
   85             2y       0.85*2y
-------------------------------------
   35            135       0.35*135
</pre>
If you continue in forming two equations in x and y you have
{{{system(x+3y=135,0.25x+0.4y+0.85*2y=0.35*135)}}}


Do what you need from that.
Maybe {{{0.25x+2.1y=47.25}}}, and make the substitution for {{{x=135-3y}}},...