\[\frac{1}{5}x - 3x = \left( \frac{1}{5} - 3 \right)x =\]
\[= \left( \frac{1}{5} - \frac{15}{5} \right)x = - \frac{14}{5}x =\]
\[= - 2\frac{4}{5}x = - 2,8x.\]