(i) Based upon values shown on decedent A's timely filed estate tax return, 60 percent of the value of A's adjusted gross estate consisted of a farm which was a closely held business within the meaning of section 6166. A's executor, B, made a protective election under section 6166 when he filed A's estate tax return. B also applied for an extension of time under section 6161 to pay $15,000 of the $30,000 of estate tax shown due on the return. The requested extension was granted and was renewed at the end of 1 year. Eighteen months after the return was filed and after examination of A's estate tax return, the value of the farm was found to constitute 67 percent of the adjusted gross estate. B entered into an agreement consenting to the values as established on examination and to a deficiency of $5,000. B then filed a final notice of election under section 6166, choosing a 5-year deferral followed by 10 annual installment payments and thereby terminated his extension under section 6161 because that amount of tax was then included under the section 6166 election. B could have extended payment of 67 percent of the total estate tax, or $23,450. $23,450 is eligible for installment payments under section 6166 and the section section 6166 election is considered to be for that amount. B is considered to have prepaid $3,450 of tax since only $20,000 of tax remained unpaid. The $3,450 is attributed to the first installment of $2,345 and to $1,105 of the second installment which would have been payable under the section 6166 election.