$.$ At the time Sherry signed her joint return, she knew that her spouse did not report $$5,000$ of gambling winnings. The IRS examined the tax return several months after she filed it and determined that her spouse's unreported gambling winnings were actually $$25,000.$ Sherry established that she did not know about, and had no reason to know about, the additional $$20,000$ because of the way her spouse handled gambling winnings. If Sherry meets the other requirements, what amount of the understated income will qualify for innocent spouse relief?