\[\boxed{\mathbf{27}\mathbf{.}}\]
\[\textbf{б)}\ 42 + 5 \cdot 6 = 42 + 30 = 72\]
\[30 - 3 \cdot 3 = 30 - 9 = 21\]
\[5 \cdot 9 - 12 = 45 - 12 = 33\]
\[35 + 18\ :2 = 35 + 9 = 44\]
\[100 - 12\ :2 = 100 - 6 = 94\]
\[40\ :5 + 92 = 8 + 92 = 100\]