A slender rod of mass m$\_$o $=11\mathrm{.}9$ kg and length l $=850$ m is welded at its midpoint A to the rim of the solid circular disk of mass m $=20$ kg and radius r $=310$ mm$.$ The center of the disk, which rolls without slipping, has a velocity v $=1\mathrm{.}7$ m$/$s at the instant when A is at the top of the disk with the rod parallel to the ground. For this instant determine the angular momentum of the combined body about O$.$ The angular momentum is positive if counterclockwise, and negative is clockwise.