3(1)Where by the Act a person is entitled(a)to make a deduction from tax payable by him,(b)to a refund of tax paid, or(c)to receive a payment from the Minister in an amount equal to tax paid,and circumstances exist that render it difficult to determine the exact amount of such deduction, refund or payment by the Minister, the amount of the deduction, refund or payment by the Minister shall, where the person consents, be determined in the manner set out in subsection (2).(2)The exact amount of deduction, refund or payment by the Minister, determined for the purpose of subsection (1), shall be equal to the tax that would have been paid at the time of imposition of the tax on the goods on a price or value determined by reducing(a)the sale price of the goods in the transactions in respect of which the deduction, refund or payment by the Minister is applied for, or(b)the contract price where the goods were used in carrying out a contract and no sale price of the goods in the transactions in respect of which the deduction, refund or payment by the Minister is applied for can be established,by a percentage thereof determined by the Minister after taking into account the class of the goods and the nature of and parties to the transaction that resulted in the application for a deduction, refund or payment by the Minister.