\[\boxed{\mathbf{39.}}\]
\[2 \cdot 6 = 12\]
\[2 + 2 + 2 + 2 + 2 + 2 = 12\]
\[3 \cdot 7 = 21\]
\[3 + 3 + 3 + 3 + 3 + 3 + 3 = 21\]
\[4 \cdot 4 = 16\]
\[4 + 4 + 4 + 4 = 16\]
\[5 \cdot 8 = 40\]
\[5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 =\]
\[= 40\]
\[6 \cdot 4 = 24\]
\[6 + 6 + 6 + 6 = 24\]
\[7 \cdot 5 = 35\]
\[7 + 7 + 7 + 7 + 7 = 35\]
\[8 \cdot 2 = 16\]
\[8 + 8 = 16\]
\[9 \cdot 5 = 45\]
\[9 + 9 + 9 + 9 + 9 = 45\]
\[10 \cdot 3 = 30\]
\[10 + 10 + 10 = 30\]