Решение:
$$9\frac{1}{6} : 4\frac{4}{5} = 51\frac{9}{16} : x$$
$$\frac{55}{6} : \frac{24}{5} = \frac{825}{16} : x$$
$$\frac{55}{6}x = \frac{24}{5} \cdot \frac{825}{16}$$
$$\frac{55}{6}x = \frac{19800}{80}$$
$$x = \frac{19800}{80} : \frac{55}{6}$$
$$x = \frac{19800}{80} \cdot \frac{6}{55}$$
$$x = \frac{118800}{4400}$$
$$x = 27$$
Ответ: $$x = 27$$