知3x+7y+z=315,4x+10y+z=420,求x+y+z=?越快越好!

已知3x+7y+z=315和4x+10y+z=420,求x+y+z 谢了3x+7y+z=315 4x+10y+z=4203x+7y+z=3154x+10y+z=420 知3x+7y+z=315,4x+10y+z=420,求x+y+z=?越快越好! 若3x+7y+z=5,4x+10y+z=3,则x+y+z=? 解方程组：3x+7y+z=31.5,4x+10y+z=42求 x+y+z 已知x、y、z满足{3x+7y+z=5 ,求x+y+z的值 {4x+10y+z=3 已知x,y,z满足3x+7y+z=5 4x+10y+z=3 求x+y+z的值 已知4x-3y-6z=0,x+2y-7z=0,求5x+2y-z/2x-3y-10z 已知,方程组:4x-3y-7z=0 x+2y=10z 则(x-y+z)÷(x+y+z)=—— (4x-2y-z)-{5x-[8y-2z-(x-2y)]-x-(3y-10z)}=? 请高手帮我解几道3元1次的方程组!好的100分,x+2y+3z=15x-y+7z=20x+3y+2z=14x+y-z=3y+z-x=5z+x-y=7x+y-z=0.5x-3y+2z=03x+2y-z=23x-2y=12y+3z=2x+5z=315x-3y+2z=13x+4y-z=-18z=136x-y-z=32x-4y+8z=53x-6y-z=10x+y=3y+z=5x+z=6 (4x-2y-z)-{5x[8y-2y-(x+y)]-x+(3y-10z)]=? kuaihuajian 2x+z=10 x+y-z=4 3x-y-z=0 {2x+y=10 {x-y+z=4 {3x-y-z=0 若3x+7y+z=315,4x+10y+z=420,则x+y+z=________________.  9、若3x+7y+z=315,4x+10y+z=420,则x+y+z=________________. 三元一次方程组 但只有两个方程式3x+7y+z=315 4x+10y+z=420 求x+y+z=? (4x-2y-z)-{5x-[8y-2z-(x+y)]-2(3y-10z)}=?好难啊