\[\boxed{\mathbf{5.}}\]
\[6 \cdot 7 = 42\]
\[42\ :6 = 7\]
\[6 \cdot 8 = 48\]
\[48\ :6 = 8\]
\[6 \cdot 9 = 54\]
\[54\ :6 = 9\]
\[6 \cdot 10 = 60\]
\[60\ :6 = 10\]