Решим уравнение:
$$\frac{21}{25} = \frac{49}{50x}$$
$$50x = \frac{49 \cdot 25}{21}$$
$$50x = \frac{7 \cdot 25}{3}$$
$$50x = \frac{175}{3}$$
$$x = \frac{175}{3} : 50$$
$$x = \frac{175}{3} \cdot \frac{1}{50}$$
$$x = \frac{7}{3} \cdot \frac{1}{2}$$
$$x = \frac{7}{6}$$
$$x = 1 \frac{1}{6}$$
Ответ: $$1 \frac{1}{6}$$