The expression 'purchase price ' is defined in section 2(gg) of the Act as follows: "2(gg) 'purchase price ' means the amount of valuable consideration paid or payable by a person for the purchase of any goods, less any sum allowed by the seller as cash discount according to trade practice and shall include any sum charged for anything done by the seller in respect of the goods at the time of or before, delivery thereof, other than the cost of freight or delivery or the cost of installation when such cost is separately charged;" The expression 'turnover of purchases ' is defined in section 2(ii) of the Act thus: "2(ii) 'turnover of purchases ' with its cognate expressions means the aggregate of the amounts of purchase price paid of payable by a dealer in respect of purchase of goods made by or through him after deducting the amount, if any refunded to the dealer by the seller in respect of any goods returned to such seller within such period as may be prescribed;" 711 Section 3 F of the Act which provides for the levy of additional tax on certain dealers was introduced into the Act by U.P. Act No. 3 of 1971.