The ornamental design for seat and back cushions for a chair, as shown and described.
FIG. 1 is a perspective view of seat and back cushions for a chair showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left elevational view thereof;
FIG. 5 is a right elevational view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
In the drawings, the thick dotted lines on a surface of the seat and back cushions are sewing threads. The solid line between the two adjacent thick broken lines is a connecting line on the surface of the seat and back cushions. Both are parts of the present design.
The thin dotted lines outside the seat and back cushions, which depict the support frames of the chair, are not part of the present design.