x/2=y/3 => x=2/3y -------(1)
y/3=z/5 => z=5/3y ------(2)
将（1）（2）代入3x-y+2z=26中
3*2/3y-y+2*5/3y=y+10/3y=13/3y=26 => y=6 => x=4 z=10