A non-uniform girder $MN$ has length 150 cm and mass 18 kg. A worker places a toolkit of mass 12 kg on the girder at $L$, where $ML=30$ cm. The girder is held in horizontal equilibrium by two vertical supports at $M$ and $N$ providing tensions $T_M$ and $T_N$.

Given that the tension $T_N$ is 12 N greater than the tension $T_M$.