The ornamental design for a panel, as shown and described.
FIG. 1 is a perspective view of a panel.
FIG. 2 is a front elevational view of the panel of FIG. 1.
FIG. 3 is a back elevational view of the panel of FIG. 1.
FIG. 4 is a side elevational view of the panel of FIG. 1.
FIG. 5 is a side elevational view of the panel of FIG. 1 from the opposite side from FIG. 4.
FIG. 6 is a top plan view of the panel of FIG. 1.
FIG. 7 is a bottom plan view of the panel of FIG. 1; and,
FIG. 8 is a perspective view of the panel of FIG. 1 sitting within the interior of a semi-truck cab.
The broken lines in FIGS. 1-7 depict portions of the panel that form no part of the claimed design. The broken lines in FIG. 8 showing the interior of a semi-truck cab, depict environment that forms no part of the claimed design.