Ms. Zhang, a single taxpayer, purchased her principal residence in 2015 and financed the purchase with a mortgage secured by the residence. In 2021, the average balance of the mortgage was $1,500,000, and Ms. Zhang paid $30,000 of mortgage interest. Compute Ms. Zhang's potential itemized deduction for her home mortgage interest in 2021. Group of answer choices $0 $15,000 $20,000 $30,000