In any case, while looking through the FAQs to find an existing explanation of how to find out about a style ID, I noticed that "How do I make a custom style?" (http://www.livejournal.com/support/faqbrowse.bml?faqid=128) says,
You can either create a blank style, or base your style off an existing system style template.
In reality, you can also base it off a style someone else made, as long as they marked it as 'public' and you know its style ID.
So, there are three suggestions I can make:
a) In FAQ #128, add the info that you can base your style off other styles if they are made public. Add information how to find out about a style's ID - either through the style browser, or by asking the friend to look at /styles/edit.bml which lists all their styles with IDs. Then, in FAQ #146, link to #128 saying, "Look at #128 to learn how to find out the style ID".
b) Add the explanation to FAQ #146 instead. Optionally link to it from #128, although that's silly.
c) Make an entire new FAQ "How do I find out about a style ID?", but that seems unnecessary...