The ornamental design of an expandablerack for a sink, as shown and described.
FIG. 1 is a perspective view of an expandable rack for a sink in an expanded condition in accordance with my design.
FIG. 2 is a perspective view of the expandable rack for a sink in a collapsed condition;
FIG. 3 is a top plan view thereof in the collapsed condition;
FIG. 4 is a front elevational view thereof in the collapsed condition, with the rear elevational view being substantially identical;
FIG. 5 is a side elevational view thereof viewed from the left side in FIG. 2, with the right side elevational view being substantially identical; and,
FIG. 6 is a bottom plan view of the expandable rack for a sink in the collapsed condition.