This section is from the book "School Needlework. A Course of Study in Sewing designed for use in Schools", by Olive C. Hapgood. Also available from Amazon: School Needlework: A Course Of Study In Sewing Designed For Use In Schools.
A placket is an opening made in a garment.
1. At the middle of the side not hemmed, cut three inches by a thread.
2. Hold the wrong side of the cloth towards you.
3. At the left of the opening, make a hem turned to a point at the bottom, and one-eighth of an inch wide at the top.
4. At the right, make a hem three-fourths of an inch wide the entire length.
5. Turn to the right side of the cloth.
6. At the bottom of the wide hem make a horizontal crease by a thread.
7. On the right side of the opening, make a vertical crease by a thread, three-fourths of an inch from the edge.
8. Place the edge of the wide hem on this crease.
9. Holding the hem carefully, baste with small stitches, on the horizontal crease.
What is a placket? When the wrong side is towards you, how wide a hem is made at the left? How wide at the right? How many rows of stitching are taken in tacking the hem?