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?

A. $2,500

B. $5,000

C. $10,000

D. $20,000