Rotational Motion Part 2

Two discs of moment of inertia I1=4‌kg‌m2 and I2=2‌kg‌m2 about their central axes & normal to their planes, rotating with angular speeds 10‌rad∕ s & 4‌rad∕ s respectively are brought into contact face to face with their axe of rotation coincident. The loss in kinetic energy of the system in the process is ______J.