In this Act, unless the context otherwise requires,-

(55). "turnover of sales", in relation to any period, means the aggregate of the sale-prices or parts of sale-prices received or receivable by a dealer in respect of sales as defined in clause (39) of the Act and in clause (g) of section 2 of the Central Sales Tax Act, 1956, of goods made during such period after deducting therefrom –

(a) the sale-prices or the parts of sale-prices, if any, in respect of sales of goods during such period, which are shown to the satisfaction of the Commissioner to have been purchased by the dealer in West Bengal, upon payment of tax on the maximum retail price of such goods or, where tax on maximum retail price of such goods were paid in West Bengal in an earlier occasion, and

(b) the amounts, if any, refunded by the dealer in respect of any such goods returned or rejected by the purchaser within six months from the date of such sales;