Shape armhole/neck

Hi I’ve had some great help from my last posts I was hoping I could get some help again

My pattern says shape armhole- cast off 9 sts at beg of next row 69sts
Work 13 rows stk tie a colored thread at beg of last row.

Shape neck - dec at end of next and alt rows until 51 sts remain
Work 1 row. Cast off loosely

My problem is with the neck part

How do I decrease??
Do I start dec at the next row of the one I tied the thread to and the every alt row after that??

Tia

“tie a colored thread at beg of LAST row…
dec at end of NEXT and alt rows until 51 sts remain.”

Yes, that’s right or in other words;
Cast off 9 sts (call this row 1), work 13 rows (the last row will be row 14, it has the colored thread at its beginning), work across row 15 and 3sts from the end, dec. That will give you one edge stitch and place the dec one stitch in from the edge making a neater edging.

Thank you for that by dec do they mean k2t??

K2tog will work. Is this the left front of a cardigan (ledt as you would wear it)? The k2t will slant to the right which matches the shape at the neck. A ssk works well for the same shaping on the right front because it slants left. Both are shown on the Glossary tab at the top of this page.