Rotational Motion: JEE Main 2019 Physics question

Two coaxial discs, having moments of inertia I₁ and I₁/2, are rotating with respective angular velocities $\omega$_1 and $\omega$₁/2 , about their common axis. They are brought in contact with each other and thereafter they rotate with a common angular velocity. If E_f and E_i are the final and initial total energies, then (E_f - E_i) is: