\[5x - 3a = 2\]
\[5x = 2 + 3a\]
\[x = \frac{2 + 3a}{5}\]
\[\frac{2 + 3a}{5} < 0\]
\[2 + 3a < 0\]
\[3a < - 2\]
\[a < - \frac{2}{3}.\]