here's an easy way to tell if you should use who or whom. I teach this to my students, because if you say "subject" or "object" to them, they get all glassy eyed:
Rewrite the sentence with he/him instead. So if your question is, "Who/whom will take me to the store?" You would rewrite it as "He will take me to the store." If the question is something like, "We asked our teacher, who/whom we had just met," you would rewrite the second half of the sentence as "We had just met him."
If the sentence works with "he," the answer is always "who." If the sentence works with "him" it will always be "whom." (Get it? him=whom). You can do it with she/her, too, of course, but it's much easier to remember this way.
Lisa is right about further/farther. But generally farther=distance (remember "far") and "further" usually refers to time or amount.
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