Row Reduction & Rank · Medium problem

Three weights $m_1,m_2,m_3$ (kg) on a balance satisfy $m_1+m_2+m_3=60$ (total mass) and $m_1-2m_2+m_3=0$ (torque balance about the pivot). Also, $m_1$ is $5$ kg less than $m_2$. Find $m_3$.