A $2\text{ kg}$ mass is placed with its center of mass at $x= -10 \text{ cm}$ to the left of the fulcrum on a balance beam, as shown above. Two identical masses $m$ are placed with their centers of mass at $x=40\text{ cm}$ and $x=70\text{ cm}$ to the right of the fulcrum. The mass of the balance beam is negligible.

What must be the value of $m$ in order for the system to be in rotational equilibrium?