Help! Pattern doesn't make sense, beginner here

Please help! I’m newly started as a knitter and am trying to knit a stylecraft pattern for some bootees. I’ve followed it to the point where the maths doesn’t add up! Cast on 35, then after a few rows: k19 turn, k9 and continue 11 rows. Fine so far! Then: with rs facing pick up and knit 10 sts from side to instep, 9 sts from needle, 10 sts from other side And Knit Across Rem 10 sts. 49sts.
Where do remaining sts come from???

Thank you in advance for putting me out of my misery!!

(35) = 35
(19) turn, 16 = 35
10, (9) turn, 16 = 35
10, (PO 10), (9), (PO10), 16 = 55

Seems you start with 35. Then you do some short row work where you work on 19sts then 9sts, leaving 16 and 10 on either end. Then you PO 10 along the sides of the 11 rows you worked, thus adding 20 sts. That should either give you 39 (PO10, K9, PO10, K remaining 10) or 55 (original 35 + 20) depending on what all is included in the count.
From what you wrote I think they meant 39 NOT 49 and they have not yet accounted for the 16sts still hanging out in left fieled after your first short row turn.

Could you provide the actual pattern name or link please?

Hi and welcome to Knitting Help!
Yes, a link to the pattern if possible would be helpful. Possibly thisone? What concerns me is the asymmetry after you knit 19, turn and knit 9. That leaves you 10sts on one side of the instep and 16 on the other side. Is it possible that the cast on is 29sts? Then you would have 10sts on one end, 10sts picked up on the instep, 9sts at the toe, 10sts picked up down the other side of the instep and [I]10sts[/I] on the other end which totals 49sts.