Ribbing directions

I am not sure I understand these direction and I hope someone can help.

" cast on 20 sts work ribbing k1p1 for 5 cm. At the end of last row cast on 18 sts and content to work ribbing until entire edge meas 10 cm"

can anyone clarify for me? Am I knitting until new section measures 10 cm?

I think that you knit until it’s 10cm from the original cast on sts.

Ok thanks. I wasn’t sure since it states states “until entire piece meas 10”

Right, ‘entire piece’ seems like it would be the whole thing, not just from the second cast on.

Ok so the new cast add on will be 5 inches when the original measures 10 and I stop there?

That’s what it sounds like. What are you making - what’s the pattern?

Thanks so much!
making a baby jump suit. However I think it may be too hard for me. It was just so darn cute.:muah: