DON'T!
DO NOT cross-RSS feeds between sites on the network! Not on a self-hosted one certainly.
However it looks like you're hosted on WordPress.com and not a self hosted site.
It can be very confusing, but generally we can't help you with issues on WordPress.com because their system is more limited as to what you can and cannot edit.
You should post this question on http://en.support.wordpress.com/If you're curious about the differences between .com and .org, please read this: http://en.support.wordpress.com/com-vs-org/