How do I know if my machine needs horizontal or vertical feet?

Hi everyone, I'm new to sewing and have a question.  I want to buy a walking foot for my machine, but don't know how to tell if it is horizontal or vertical?  The manual doesn't say.

It's a Kenmore Drop-In Bobbin Sewing Machine - 90 Stitch Functions, Built-in 1-Step Buttonhole Item# 02016231000 Model# 16231
This is the link.http://www.sears.com/shc/s/p_10153_12605_02016231000P?keyword=sewing+machine#descriptionAnchor

Thanks in advance for your help.

If it's a drop-in bobbin then it's a horizontal hook.  The hook refers to how the bobbin sits.  If the bobbin is vertical either in the front or side of the machine then it's vertical.  If the bobbin simply drops into the case then it's horizontal.

Thank you very much!