What is the value of the torque required so that the disc reaches its final speed from rest?

Question

The figure above shows the angular velocity variation of rotating disc, having a mass of 1 kg and radius 1m. What is the value of the torque required so that the disc reaches its final speed from rest?

         (a) 10 Nm                       (b) 5 Nm                      (c) 8 Nm                      (d) 2 Nm