Niles and Marsha adopted an infant boy (a U.S. citizen). They paid $15,500 in 2020 for adoption-related expenses. The adoption was finalized in early 2021. Marsha received $4,000 of employer-provided adoption benefits. For question (a), assume that any adoption credit is not limited by modified AGI or by the amount of tax liability. a. What amount of adoption credit, if any, can Niles and Marsha take in 2021 ? b. Using the information in (a), assume that their modified AGI was $223,000 in 2021. What amount of adoption credit is permitted in 2021