help with neck shape

[mima]

Hi,
I'm a new member and I hope you can help me. I'm working on this free pattern: http://www.lionbrand.com/patterns/60448.html?noImages=
I am at the point where I need to shape the neck on the back piece, here is what the pattern says:

Continue in Color Stripe Pattern across 13 (15, 17, 20, 24)