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 part $($a$),$ assume that any adoption credit is not limited by modified AGI or by the amount of tax liability.

What amount of adoption credit, if any, can Niles and Marsha take in $2021?$

Using the information in part $($a$),$ assume that their modified AGI was $$223,000$ in $2021.$ What amount of adoption credit is allowed in $2021?$