Suppose 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 his spouse, 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.