\[\boxed{\mathbf{4.13}}\]
\[\textbf{а)}\ 72\ :8 = 9 + 51 = 60\ :15 =\]
\[= 4 \cdot 9 = 36 + 14 = 50\]
\[\textbf{б)}\ 56\ :7 = 8 \cdot 5 = 40 - 13 =\]
\[= 27\ :9 = 3 + 17 = 20\]
\[\textbf{в)}\ 63\ :9 = 7 + 33 = 40\ :8 =\]
\[= 5 \cdot 13 = 65 - 25 = 40\]
\[\textbf{г)}\ 54\ :6 = 9 \cdot 7 = 63 + 17 =\]
\[= 80\ :10 = 8 - 8 = 0\]
\[\textbf{д)}\ 81\ :9 = 9 + 41 = 50\ :5 =\]
\[= 10 \cdot 7 = 70 - 17 = 53\]