Two discs of moment of inertia I_1=4 kg m^2 and I_2=2 kg m^2, about their central axes & normal to their planes, rotating with angular speeds 10 rad…

Two discs of moment of inertia $\displaystyle I_1=4 \mathrm{~kg} \mathrm{~m}^2$ and $\displaystyle I_2=2 \mathrm{~kg} \mathrm{~m}^2$, about their central axes & normal to their planes, rotating with angular speeds $\displaystyle 10 \mathrm{rad} / \mathrm{s}$ & $\displaystyle 4 \mathrm{rad} / \mathrm{s}$ 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 $\displaystyle \_\_\_\_$ J.