a)
5x+7z-3y-8y+4z-6x=5x-6x-3y-8y+7z+4z=-x-11y+11z
b)
4xz+2x-6xy+3x-xy-4xz=2x+3x-6xy-xy+4xz-4xz=5x-7xy
[tex]c)\\14a^{2}+20a^{3}-15a^{2}+a-20a^{3}-2a=-a^{2}-a[/tex]
