Pattern Help!

I’m new to reading patterns so I get easily confused. I know most abbreviations and the basic stitches.
The pattern that I am trying to read (Drops Moon Socks) is really confusing me. This is the part I am up to.

When 7-8.5-10cm have been worked, bind off starting on a RS row 1 edge st in each side, by binding off 1 st in the beg of next 2 rows =9-11-11

Help! and for those who want to see the pattern.

Welcome to KH. When your work is the specified length bind off 1 stitch at the beginning of the next two rows.

[B]7-8.5-10cm[/B] Each of the three numbers correspond to the sizes, 7 for the smallest, 8.5 for medium, 10 for the largest.

Thanks for the link, X.