Angular Momentum & its Conservation question from JEE Main 2024 (30 Jan, Shift 2)

Two discs of moment of inertia $I_1 = 4\text{ kg m}^{2}$ and $I_2 = 2\text{ kg m}^{2}$, about their central axes & normal to their planes, rotating with angular speeds $10\text{ rad/s}$ & $4\text{ rad/s}$ respectively are brought into contact face to face with their axes of rotation coincident. The loss in kinetic energy of the system in the process is _________ J.