Joining the RB & LB
The back pieces RB and LB are now joined.
On the left is the RB, on the right is the LB, which is still connected to your working yarn from the last wrong side row.
Start the right side row with the LB as follows:
selvedge st, [Sizes 3, 5, 6, 7, 8 only: M1L for armhole inc] (Size 9 only: M2L), work all remaining sts of LB in established rib pattern (including the selvedge st), cast on 6 (4) 10 (14) 18 (14) 20 (26) 26 sts using the Backward Loop On.
Pick up the RB, make sure it is facing you the right way.
Work all sts in established rib pattern until the selvedge st, [Sizes 3, 5, 6, 7, 8 only: M1R for armhole inc] (Size 9 only: M2R), selvedge st.
The back pieces are now joined.
Knit the wrong side row in established rib pattern, including the new sts and a selvedge st on either side.
Continue to work flat in established rib pattern with a selvedge st on both sides.
Refer to the instructions for your size on how to work the armhole inc.