Confused with bind off and place markers

What does it mean when it says Cast off 39 sts placing markers to indicate back of neck at each side of center [27]—where do I place the markers? Thank you

You need to place your back of neck markers to cover the center 27 sts of the 39 cast off sts so cast off 6sts,put a marker here, cast off the next 27sts, put a marker here and cast off the next 6 sts.
Hope this helps.