Vince and Millie are married. Vince dies this year with a gross estate of $25 million and no adjusted prior gifts. Calculate the amount of estate tax due (if any) under the following alternative conditions:
a) Vince leaves his entire estate to Millie.
b) Vince leaves $10 million to Millie and the remainder to charity.
c) Vince leaves $10 million to Millie and the remainder to his son, Paul.
d) Vince leaves $10 million to Millie and the remainder to a trust whose trustee is required to pay income to Millie for her life and the remainder to Paul.