Steps:

1. Draw an 80-unit square. (Enter “D” for dimension)
2. Connect the diagonal lines.
3. Use the offset command to draw lines, 10 units apart.
4. Trim excess outline lines.
5. Select internal intersections to create a rectangle. (Observe the guided line and intersections by hovering the cursor over an object snap location.)
6. Remove unnecessary lines.
7. Add annotations.