If I've read the row right, it looks like this part,insert needle purl ways through back of 2nd st then 1st st and slip both sts off needle tog, purl next st then pass 2 slipped sts tog over purl st, will reduce you down to your 87 sts. And it looks like you're crossing/twisting those 2 slipped stitches by picking the 2nd st up first, then the 1st one, before passing those slipped sts over the p1.
If the passing the slipped stitches part is the confusing one, check the knitting tips page for psso under the free videos tab. I'm pretty sure there's an example there.
Also check for notes somewhere in your pattern that may explain this stitch combination. yft may be bring yarn to front, but check the stitch definitions in your pattern to be sure. Hope this was of some help, and I'll defer to the others when they inevitably chime in.
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