Knitting Pattern Question

I am working on this baby sweater. It is done in a check pattern that goes over (a multiple of 6 plus 3). I've got the back done up to the point where I'm supposed to decrease for the armholes, and I'm confused about how to maintain the pattern, since they are telling me to cast off 7 stitches at the start of the next two rows. This will leave me with stitches not equal to  (a multiple of 6 plus 3). Since the check pattern includes yarn overs and k2tog etc., it doesn't seem to just be a matter of starting/ending partway through a repeat.

Help! Can someone help! :D