The tax payable by a dealer, who is liable to pay tax on his turnover of purchases under section 11 or section 12, shall be levied—

(a) at the rate of two per centum of such part of the turnover of purchases of raw jute under section 11 as defined in sub-clause (a) and sub-clause (b) of clause (54) of section 2; or

(b) at the rate of tax as applicable to a sale of such goods under sub-section (2) of section 16 on such part of the turnover of purchases as represents purchases under section 12 as defined in sub-clause (c) of clause (54) of section 2:

Provided that in calculating the tax payable under the clause (a) by a dealer, who is the occupier of a jute mill, on his turnover of purchases of raw jute during the period, the purchase price in respect of any quantity of raw jute sold and despatched by him during such period subsequent to his purchase thereof to any place within West Bengal shall be deducted from such turnover of purchases.