Two discs are rotating about their respective axes, which are normal to the discs and pass through their centres. Disc \(D_1\) has a \(2\) kg mass and \(0.2\) m radius and an initial angular velocity of \(50~\text{rad} ~\text{s}^{-1}.\) Disc \(D_2\) has a \(4\) kg mass, \(0.1\) m radius and an initial angular velocity of \(200~\text{rad} ~\text{s}^{-1}.\) The two discs are brought into contact face to face, with their axes of rotation coincident. The final angular velocity (in \(\text{rad} ~\text{s}^{-1}\)) of the combined system is:
1. \(60\)
2. \(100\)
3. \(120\)
4. \(40\)