solve only part b for 2021. please show work

58. Roland had a taxable estate of $15.5 million when he died this year. Calculate the amount of estate tax due (if any) under the following alternatives a) Roland's prior taxable gifts consist of a taxable gift of $1 million in 2005 b) Roland's prior taxable gifts consist of a taxable gift of $1.5 million in 2005 c) Explain how the tax calculation would change if Roland made a $1 million taxable gift in the year prior to his death