\[3x² - 124x - 84 = 0\]
\[D = 15\ 376 + 1008 =\]
\[= 16\ 384 = 128²\]
\[x_{1,2} = \frac{124 \pm 128}{6} = 42;\ - \frac{2}{3}\]
\[Ответы:\ 42;\ - \frac{2}{3}\text{.\ }\]