$4\frac{3}{4} : 7\frac{1}{8} = х : 12$
$х = 4\frac{3}{4} * 12 : 7\frac{1}{8}$
$х = \frac{19}{4} * 12 * \frac{8}{57}$
$х = 57 * \frac{8}{57}$
$х = 8$

$6\frac{1}{2} : х = 6\frac{5}{6} : 4,1$
$х = 6\frac{1}{2} * 4,1 : 6\frac{5}{6}$
$х = \frac{13}{2} * \frac{41}{10} * \frac{6}{41}$
$х = \frac{13}{2} * \frac{1}{5} * \frac{3}{1}$
$х = \frac{39}{10} = 3,9$