x/150+y/200+(3000-x-y)/240=31
8x+6y+5*(3000-x-y)=31*1200
8x+6y+15000-5x-5y=31*1200
3x+y=22200 （1)
(3000-x-y)/150+y/200+x/240=31,
8*(3000-x-y)+6y+5x=31*1200
24000-8x-8y+6y+5x=31*1200
-3x-2y=13200 (2)
由(1)+(2)得
-y=35400
y=-35400
x=19200