x+y+z=142 .(1)x/28+y/30+z/35=4.5 .(2)x/35+y/30+z/28=4+42/60=4.7.(3)(3)-(2):7/(28*35)*(z-x)=0.2z-x=28.(4)(1)-(2)*30:-2x/28+5z/35=7-x+2z=982z-x=98.(5)(5)-(4):z=70代入(4):x=z-28=42代入(1):42+y+70=142,y=1...