$4 : 6 = \frac{4}{6} = \frac{2}{3} = \frac{10}{15}$
$11 : 15 = \frac{11}{15}$
$\frac{10}{15} < \frac{11}{15}$, значит:
4 : 6 < 11 : 15

$112 : 64 = \frac{112}{64} = \frac{7}{4}$
$9 : 4 = \frac{9}{4}$
$\frac{7}{4} < \frac{9}{4}$, значит:
112 : 64 < 9 : 4

$72 : 144 = \frac{72}{144} = \frac{1}{2}$
$36 : 108 = \frac{36}{108} = \frac{1}{3}$
$\frac{1}{2} > \frac{1}{3}$, значит:
72 : 144 > 36 : 108

$81 : 45 = \frac{81}{45} = \frac{9}{5} = \frac{54}{30}$
$56 : 48 = \frac{56}{48} = \frac{7}{6} = \frac{35}{30}$
$\frac{54}{30} > \frac{35}{30}$, значит:
81 : 45 > 56 : 48