\[\boxed{\mathbf{13}\mathbf{.}}\]
\[\textbf{а)}\ 17 + 2 \cdot 2 = 17 + 4 = 21\]
\[16 + 2 \cdot 3 = 16 + 6 = 22\]
\[19 + 4\ :2 = 19 + 2 = 21\]
\[18 + 8\ :2 = 18 + 4 = 22\]
\[\textbf{б)}\ 75 + 2 \cdot 4 = 75 + 8 = 83\]
\[89 + 18\ :2 = 89 + 9 = 98\]