Two disks are mounted on low-friction bearings on the same axle and can be brought together so that they couple and rotate as one unit. The first disk, with a rotational inertia of 2.508 kg-m^2 about its central axis, is initially spinning at a rate of 621 rpm. The second disk , with a rotational inertia of 4.092 kg-m^2 about its central axis, is initially spinning at a rate of 684 rpm in the same direction as the first one. They then couple together a) What is their angular speed after coupling? b) If the second disk is initially spinning opposite to the first one , what is the angular speed after coupling ?