Реши уравнение y-4/7*y=4,2.

\[y - \frac{4}{7}y = 4,2\]

\[y\left( 1 - \frac{4}{7} \right) = 4,2\]

\[y\left( \frac{7}{7} - \frac{4}{7} \right) = 4,2\]

\[\frac{3}{7}y = 4,2\]

\[y = 4,2\ :\frac{3}{7} = \frac{42}{10} \cdot \frac{7}{3}\]

\[y = \frac{3 \cdot 2 \cdot 7 \cdot 7}{5 \cdot 2 \cdot 3} = \frac{49}{5}\]

\[y = 9\frac{4}{5} = 9,8.\]

\[Ответ:\ y = 9,8.\]