which this chapter becomes effective, the applicable percentage of the price for which such product is sold, and (2) for any product sold during any calendar year after the period described in paragraph (1), the applicable equivalent rate. (b) Applicable percentage For purposes of subsection (a)(1), the applicable percentage shall be determined as follows: (1) For any marijuana product sold during the first 2 calendar years in which this chapter becomes effective, 10 percent. (2) For any marijuana product sold during the calendar year after the period described in paragraph (1), 15 percent. (3) For any marijuana product sold during the calendar year after the period described in paragraph (2), 20 percent. (4) For any marijuana product sold during the calendar year after the period described in paragraph (3), 25 percent. (c) Applicable equivalent rate (1) In general For purposes of subsection (a)(2), the applicable equivalent rate for each calendar year shall be equal to— (A) in the case of any marijuana product not described in subparagraph (B) which is sold during such year, the applicable rate per ounce of such product (and a proportionate tax at the like rate on all fractional parts of an ounce of such product), and (B) in the case of any marijuana product containing a marijuana derivative which is sold during such year, the applicable rate per gram of tetrahydrocannabinol in such product (and a proportionate tax at the like rate on all fractional parts of a gram of tetrahydrocannabinol in such product). (2) Applicable rate (A) In general For purposes of paragraph (1)(A), the applicable rate per ounce for any calendar year shall be equal to 25 percent of the prevailing sales price of marijuana sold in the United States during the 12-month period ending one calendar quarter before such calendar year, expressed on a per ounce basis, as determined by the Secretary. (B) Marijuana derivatives For purposes of paragraph (1)(B), the applicable rate per gram of tetrahydrocannabinol shall be equal to the quotient