D.J., who is single, had $15,000 in social security benefits in 2021. D.J's modified adjusted gross income for 2021 was $41,000. Using only the Tier 1 calculation for social security benefits, how much of DJ's social security benefits are taxable? D.J.'s base amount is $25,000. Multiple Choice $7,500 $8,000 $15,000 None of the above