In this Act, unless the context otherwise requires,-

(54). "turnover of purchases", in relation to any period, means,

(a) in case of an occupier of a jute-mill liable to pay tax under section 11, the aggregate of the purchase prices or parts of purchase prices payable by such occupier for the quantities of raw jute purchased by him during such period after deducting the amounts, if any, refunded to him by the seller during such period in respect of any quantity of raw jute returned to the seller within ninety days from the date of its purchase and such other amounts as may be prescribed,

(b) in case of a shipper of jute liable to pay tax under section 11, the aggregate of the purchase prices or parts of purchase prices payable by such shipper of jute in respect of the quantities of raw jute purchased by him in West Bengal and despatched by him during such period to any place outside West Bengal by any means of transit,

(c) in case of any dealer liable to pay tax under section 12, the aggregate of the purchase prices or parts of purchase prices payable by such dealer in respect of the goods purchased by him during such period for use of such goods in West Bengal, after deducting the amounts, if any, refunded to the seller during such period in respect of any such goods purchased but returned to the seller within six months of such purchase;