Question 1039019
x,y,z for 25%,35%,55% acid solutions


{{{z=3y}}} is given in description.


Pure acid in the result solution will be  45*90, counting in percent.


{{{system(25x+35y+55z=45*90,x+y+z=90,z=3y)}}}


Study that system and attend it to understand.  Once understood, solve the system.