Вопрос:

Ответ:

\[5x = 4y\]

\[\frac{5}{4} = \frac{y}{x};\ \ \ \ \ \frac{5}{y} = \frac{4}{x};\ \ \ \ \ \frac{x}{y} = \frac{4}{5};\ \ \ \ \ \frac{x}{4} = \frac{y}{5}.\]