The ornamental design for a rearportion of an automobile, as shown and described.
FIG. 1 is a front perspective view of a rear portion of an automobile showing our new design;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a right side elevation view thereof;
FIG. 4 is a front elevation view thereof;
FIG. 5 is a rear elevation view thereof; and,
FIG. 6 is a top plan view thereof.
The design does not appear on the side opposite that depicted in FIG. 3 and is not part of the claimed design. The portion of the vehicle in light contrast is environment and is not a part of the claimed design.