Maggie, I’m sorry that you’ve had health struggles
. Hopefully we can help you out.
Because you’re working in reverse st st, the purl rows will be your right side rows. So if you start off with the first set of instructions, you have:
Row 1 (RS): Purl
Row 2 (WS): Knit
Row 3: Purl
Row 4: Knit, decreasing one stitch at beginning (inner edge) of this row
You’re doing this decrease row every 4th row, 18 times total, so it will also be at the beginnings of rows 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, 52, 56, 60, 64, 68, 72.
At the same time, when the piece measures 16" you are going to decrease also at outer edge, 1 st every other row 4 times, then 1 st every row 4 times: 18 sts left.
You can keep these decreases also on the WS rows like the others but since they’re going to be at the outer edge, these decreases will be at the ends of WS rows. 1 stitch every other row 4 times, then 1 stitch every row 4 times.
Sorry if you had that all figured out already for the right back panel. I kind of needed to visualize it myself, too. Now for the left back, and reversing shaping.
Starting off in reverse st st with the purl rows as your RS rows, you will begin as follows:
Row 1 (RS): Purl
Row 2 (WS): Knit
Row 3: Purl
Row 4: Knit, decreasing one stitch at end (inner edge) of this row
Again, you’re doing this decrease row every 4th row, 18 times total, so it will also be at the ends of rows 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, 52, 56, 60, 64, 68, 72.
Then, like the right back, once you reach the 16" mark you’re going to do the next set of decreases, but this time at the outer edge. If you keep these decreases on the WS rows as before, this set of decreases will fall at the beginnings of the rows, every other row 4 times, then every row 4 times.
Hope this helps.