FIG. 1 is a perspective view of a seat and back unit for a chair;

FIG. 2 is a front view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a rear view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken line showing of a tubular frame and armrests in all figures is for environmental purposes only and forms no part of the claimed design.