\[\boxed{\mathbf{6.}}\]
\[70 - x = 15\]
\[70 - x = 25\]
\[70 - x = 35\]
\[80 - x = 15\]
\[80 - x = 25\]
\[80 - x = 35\]
\[90 - x = 15\]
\[90 - x = 25\]
\[90 - x = 35\]