\[\boxed{\mathbf{11.}}\]
\[6 + x = 60\]
\[6 + x = 70\]
\[6 + x = 80\]
\[7 + x = 60\]
\[7 + x = 70\]
\[7 + x = 80\]
\[8 + x = 60\]
\[8 + x = 70\]
\[8 + x = 80\]