Help with pattern for sleeves urgently please!

New to knitting jumpers and I’m struggling to understand the instructions for increasing on the sleeves. It is written as follows:

With 4.5mm needles cast on 34 sts. Work 4 rows in k2 p2 rib. Change to 5mm needles.
Next row: k3, m1, k to last 3 sts, m1, k3.
Begin with a p. Row, cont in st st and work 17 rows.
Inc as set on every foll 8th row until there are 56 sts.
Work 21 rows straight after last Inc.

The starred/italics section is the part I don’t understand. Where and how many sts do I increase on those rows? Thank you for any help!

Welcome to the forum!
You’re to increase every 8th row, so if you work the next 17rows in st st, then you would increase on rows 25,33,41,49 etc until you get to 56sts. You’ll be increasing 2 sts per increase row as you did on this row:
Next row: k3, m1, k to last 3 sts, m1, k3.

What is the name of your pattern?

Thank you! It’s the wide-stripe tunic in No. 47 of the Big and Little Knitting Projects books although I’m not a fan of stripes so it’s one colour instead. I picked up a whole bunch of the books for 50p in a charity shop!