TeX source:
\begin{array}{rclcl} -12t(t-5)-47t &=& 13t \cr -12t^2+60t-47t &=& 13t \cr -12t^2+13t &=& 13t & \vert & -13t \cr -12t^2 &=& 0 & \vert & :(-12) \cr t^2 &=& 0 & \vert & \pm \sqrt{} \cr t &=& 0 \cr \cr \mathbb{L} &=& \{0\} \end{array}