A little stumped.

[SabrinaJL]

I'm working on a hoodie, which I haven't done before. Right now I'm working on the back part and I'm not 100% sure what I'm supposed to do.

Shape neck
Knit across to first marker, bind off center sts, knit to end. (18,20,22 sts each side for shoulders)
Bind off rem sts at beg of next 2 rows.

The part in bold is what has me stumped. I understand I'll have 20 stitches on one side, 20 bound off ones in the middle and 20 on the other side. Well, what do I do from there? How do I bind off the remaining stitches if there's 20 bound off ones between them?