\[\boxed{\mathbf{43.}}\]
\[\textbf{а)}\ 16\ :2 = 8\]
\[24\ :4 = 6\]
\[21\ :3 = 7\]
\[35\ :5 = 7\]
\[18\ :2 = 9\]
\[32\ :4 = 8\]
\[28\ :4 = 7\]
\[36\ :6 = 6\]
\[42\ :7 = 6\]
\[\textbf{б)}\ 14\ :2 \cdot 5 = 7 \cdot 5 = 35\]
\[24\ :3\ :4 = 8\ :4 = 2\]
\[8 \cdot 5\ :10 = 40\ :10 = 4\]