Here are the full information of the question: She had a Form W-2G showing gambling winnings of $1,000. She tells you she won an additional $400 for which she did not receive a Form W-2G. She also mentions she had $1,200 in gambling losses.
Assuming that Linda did the gambling that subjected to federal taxation, the amount of other income that Linda should report is:
$ 1,000+ $ 400 - $ 1,200 = $200