\[\boxed{\mathbf{19}\mathbf{.}}\]
\[1)\ 6 \cdot 3 = 18\]
\[7 \cdot 3 = 21\]
\[8 \cdot 3 = 24\]
\[9 \cdot 3 = 27\]
\[2)\ 9 \cdot 4 = 36\]
\[8 \cdot 4 = 32\]
\[7 \cdot 4 = 28\]
\[6 \cdot 4 = 24\]
\[3)\ 7 \cdot 5 = 35\]
\[9 \cdot 5 = 45\]
\[6 \cdot 5 = 30\]
\[8 \cdot 5 = 40\]