How to draft a waistband pattern piece "with under Sewing Machines Parts and Sales in Los Angeles

This is my first Burdastyle pattern and I’ve never had to draw pieces that weren’t present on the pattern. They are just rectangles of course, but I don’t understand what exactly I am supposed to make.

The direction is:

“Draft the following pieces not included:
a) right waistband 17″ long, left waistband with 1 7/8″ underlap 47.5″ long, each 3.5″ wide, finished width 1 3/4″.”

Do I need to add the underlap measurement to the 47.5? I am also unsure what seam allowance to add to these waistband pieces.