If you refer to the form and filing instructions, you'd find that the number comes from F.4797.  But what you have given us so far is just one number but not where it originates from.  Without that info, the only thing I can tell you is that the entries for F.4797 are under Income > Dispositions (Schedule D, 4797, etc.) but your case may have that number coming from somewhere else.

There is more to this than the input but this is a forum for practicing tax professionals, not for fielding questions on homework or those from consumers.  You should consult your textbook or professor for further questions.