With the back right sides together, sew the center back seam from the bottom to the dot, back stitching at the dot. Clip to the dot. Trim the seam to 1/4" and zigzag the raw edge.
With the wrong side up, turn under each placket twice along the fold lines and press. Press the center back seam to the right.
Turn the garment to the right side and place the left back placket over the right. If they do not line up on top of each other, adjust the plackets along the fold lines and repress. I have found that for some garments the fold lines will need a depth of 6/8", but for most 5/8" works best. This is such a small amount that it will not throw off the fit of the garment.
Tuck under the bottom raw edge of the left placket at an angle, and baste it in place.
In a perfect world, sewing would have exact measurements, but then where would the adventure be?