Notice to importer. The Center director shall give written notice to the importer as promptly as possible after any commingling is discovered.

Highest rate applicable. Commingled merchandise shall be assessed with duty at the highest rate or rates applicable to any one kind of merchandise included in the commingling, unless:

The quantity and value of each of the kinds so included can be readily ascertained by the usual method of CBP examination or by one or more of the methods specified in General Note 3(f), Harmonized Tariff Schedule of the United States (HTSUS) (19 U.S.C. 1202), or

The conditions specified in General Note 3(f), HTSUS, are satisfied.

Time limit. To obtain the benefit of General Note 3(f), HTSUS, the importer shall, within 30 days after the date of mailing or personal delivery of the notice provided for in paragraph (a) of this section, take appropriate action as follows:

File with the Center director evidence showing performance of the commercial settlement tests specified in General Note 3(f), HTSUS; or

Perform the segregation under CBP supervision as specified in General Note 3(f), HTSUS; or

File with the Center director documentary proof which will satisfy him that the merchandise is entitled to the lower rate of duty under General Note 3(f), HTSUS.

Extension of time limit. The 30-day limit for filing the evidence specified in General Note 3(f) or for performing the segregation specified in General Note 3(f), Harmonized Tariff Schedule of the United States, may be extended by the Center director for additional periods of 30 days each, but not beyond 6 months from the date of mailing or personal delivery of the notice provided for in paragraph (a) of this section, if the importer makes written application to the Center director for each extension and gives satisfactory reasons for its allowance.