Family death that didn't get paperwork on all monies should have payed tax on in 2015. got letter from IRS in 18 about it so payed $5100.00. where does it go in taxes?"

i had money from a death in family that didn't get paperwork on and should have payed tax on in 2015. got letter from IRS this year about it so payed $5100.00 in 2018. where do i put this in taxes?"