The period of years required to amortize any unfunded liability (described in any clause of subsection (b)(2)(B) of section
1082 of this title) of any plan may be extended by the Secretary for a period of time (not in excess of 10 years) if he determines that such extension would carry out the purposes of this chapter and would provide adequate protection for participants under the plan and their beneficiaries and if he determines that the failure to permit such extension would—
In the case of a plan other than a multiemployer plan, the interest rate applicable for any plan year under any arrangement entered into by the Secretary in connection with an extension granted under this subsection shall be the greater of