\[\frac{t^{2} + 6t}{6} - \frac{2t + 3}{2} = 12\ \ \ | \cdot 6\]
\[t^{2} + 6t - 6t - 9 = 72\]
\[t^{2} = 81\]
\[t = \pm 9.\]
\[Ответ:при\ t = \pm 9.\]