\[\boxed{\mathbf{11.}}\]
\[\textbf{а)}\ 5 \cdot 6 - 3 = 30 - 3 = 27\]
\[3 + 7 \cdot 4 = 3 + 28 = 31\]
\[20 - 2 \cdot 9 = 20 - 18 = 2\]
\[\textbf{б)}\ 8 + 35\ :5 = 8 + 7 = 15\]
\[13 - 24\ :6 = 13 - 4 = 9\]
\[27\ :3 + 7 = 9 + 7 = 16\]
\[\textbf{б)}\ 100 - 7 \cdot 2 = 100 - 14 = 86\]
\[100 - 7 \cdot 3 = 100 - 21 = 79\]
\[100 - 7 \cdot 6 = 100 - 42 = 58\]