1500（50-y-z)+2100y+2500z=90000 1500x+2100(50-x-z)+2500z=90000
75000+600y+1000z=90000 15x+21(50-x-z)+25z=900
600y+1000z=15000 -6x+4z=-150
6y+10z=150 6x-4z=150
1500x+2100y+2500(50-x-y)=90000 -10x-4y=-350
6y+10z=150
6x-4z=150 6y+10z=6x-4z 6y+14z=6x
10x+4y=350 10y+7/3z+4y=350 2y+1/3z=50 6y+z=150 z=0 y=25 x=25