Question 930267
x, y, z for volume of 5,10,40 percents acid.


{{{x+y+z=18}}}.


Acid/volume=20%


{{{(5x+10y+40z)/18=20}}}



Part of the description means {{{x=y+10}}}.  Substituting into the other two equations:


{{{system(y+10+y+z=18,(5(y+10)+10y+40z)/18=20)}}};
Just simplify and solve this system for y and z, and then evaluate x.