72 − (47 − 20) : 3 = ☐; 21 : (15 − 8) * 9 = ☐.
$72 \overset{3}{-} (47 \overset{1}{-} 20) \overset{2}{:} 3 = 72 - 27 : 3 = 72 - 9 = 63$; $21 \overset{2}{:} (15 \overset{1}{-} 8) \overset{3}{*} 9 = 21 : 7 * 9 = 3 * 9 = 27$.