How do I read this pattern?

https://preview.redd.it/g9nt9o9u9edf1.png?width=474&format=png&auto=webp&s=2b54b8d02cce4ea3bb020a8ca12c45e113678191

I am knitting my first project ever, but that ofcourse comes with some confusion about the pattern. It says: wk (work) 2,5 ins (inches) in K1, P1, rib inc 15 sts evenly along the last row.
What do they mean with wk 2,5 ins?

I am sorry if the question isn't very clear. I got no clue how to decypher it. I hope someone here is able to help me understand this!