\[\boxed{\mathbf{18}\mathbf{.}}\]
\[\textbf{а)}\ 2 \cdot 6 = 12\]
\[2 \cdot 8 = 16\]
\[10\ :2 = 5\]
\[14\ :2 = 7\]
\[\textbf{б)}\ 33 - 2 \cdot 3 = 33 - 6 = 27\]
\[2 \cdot 9 + 53 = 18 + 53 = 71\]
\[42 - 18\ :2 = 42 - 9 = 33\]
\[16\ :2 + 92 = 8 + 92 = 100\]