Can someone explain to me how they got this answer please

Question 5 1/1 pts A couple currently spends $80,000 per year for all their living expenses. Only one spouse works while the other spouse stays at home with the children. Upon the death of the working spouse, they want a life insurance policy whereby the proceeds could be invested in a tax-free municipal bond fund that would yield enough tax-free cash each year to pay the entire $80,000 of expenses (i.e. the non- working spouse would not have to return to work, and there would be sufficient funds on his/her death to leave some inheritance to the kids) They assume that the yield on municipal bond funds will be 4%. How much insurance should they purchase? $800,000 Correct! $2,000,000 $1,000,000 $40,000 Question 6 1/1 pts