Joel and Rachel are both retired. Married for 35 years, they've amassed an estate worth $12.8 million. The couple has no trusts or other types of tax-sheltered assets. If Joel or Rachel dies in 2021 , how much federal estate tax would the surviving spouse have to pay, assuming that the estate is taxed at the 40 percent rate? Note: Leave no cells blank - be certain to enter " 0 " wherever required