Net External Torque and Angular Velocity

A student on a frictionless rotating platform holds two 2.0 kg masses, each 0.5 m from the axis of rotation. The system rotates at an angular velocity of 3.0 rad/s. The student then moves the masses outward to a distance of 1.0 m from the axis. What is the net external torque required to maintain the system’s angular velocity at 3.0 rad/s?