[tex]\displaystyle\bf\\
b)\\
\overline{xy}+\overline{yz}+\overline{zx}=\\\\
=10x+y+10y+z+10z+x=\\\\
=10x+x+10y+y+10z+z=\\\\
11x+11y+11z=\boxed{\bf11(x+y+z)}\\\\\\
c)\\
\overline{xz}+\overline{zy}+\overline{yx}=\\\\
10x+z+10z+y+10y+x=\\\\
10x+x+10z+z+10y+y=\\\\
11x+11z+11y=11(x+z+y)=\boxed{\bf11(x+y+z)}[/tex]
