\[\boxed{\text{21.}}\]
\[2\ м;8\ кг;3\ м\ 60\ см.\]
\[\boxed{\text{22.}}\]
\[70\ :7 = 10\]
\[35\ :7 = 5\]
\[63\ :7 = 9\]
\[42\ :7 = 6\]
\[28\ :7 = 4\]
\[49\ :7 = 7\]
\[21\ :7 = 3\]
\[56\ :7 = 8\]
\[3 \cdot 6 = 18\]
\[4 \cdot 6 = 24\]
\[5 \cdot 6 = 30\]
\[8 \cdot 6 = 48\]
\[10 \cdot 6 = 60\]
\[7 \cdot 6 = 42\]
\[4 \cdot 6 = 24\]
\[9 \cdot 6 = 56\]
\[\boxed{\text{23.}}\]
\[350 + 20 = 370\]
\[200 + 800 = 1000\]
\[900 - 150 = 750\]
\[540 - 20 = 520\]
\[620 + 17 = 637\]
\[1000 - 1 = 999\]