Determination of value where value can not be determined under rules 3, 4 and 5.
If the value of imported goods cannot be determined under the provisions of rules 3, 4 and 5, the value shall be determined under the provisions of rule 7 or, when the value cannot be determined under that rule, under rule 8.
Provided that at the request of the importer, and with the approval of the proper officer, the order of application of rules 7 and 8 shall be reversed.