(50*8=400;500-400=100;14-8=6;21-8=13)100=6x+13yx=1;y=7.23x=2;y=6.76x=3;y=6.3x=4;y=5.84x=5;y=5.38x=6,y=4.92x=7;y=4.46x=8;y=421元4包;14元8包;8元50-4-8=38包验算:4*21+8*14+38*8=500
x+y+z=508x+14y+21z=500x=38 y=8 z=4