\[\boxed{\mathbf{23.}}\]
\[18\ :6 = 3\]
\[6 \cdot 3 = 18\]
\[24\ :6 = 4\]
\[6 \cdot 4 = 24\]
\[30\ :6 = 5\]
\[6 \cdot 5 = 30\]
\[42\ :6 = 7\]
\[6 \cdot 7 = 42\]
\[36\ :6 = 6\]
\[6 \cdot 6 = 36\]
\[48\ :6 = 8\]
\[6 \cdot 8 = 48\]
\[54\ :6 = 9\]
\[6 \cdot 9 = 54\]
\[6\ :6 = 1\]
\[6 \cdot 1 = 6\]
\[60\ :6 = 10\]
\[6 \cdot 10 = 60\]