\[5x^{2} + mx - 12 = 0;\ \ \ \ x_{1} = - 3\]
\[x_{1} \cdot x_{2} = - \frac{12}{5}\]
\[- 3x_{2} = - \frac{12}{5}\]
\[x_{2} = \frac{4}{5} = 0,8.\]
\[x_{1} + x_{2} = - \frac{m}{5}\]
\[- 3 + 0,8 = - \frac{m}{5}\]
\[- 2,2 = - \frac{m}{5}\]
\[m = 11.\]
\[Ответ:x_{2} = 0,8;\ \ m = 11.\]