(1) The tax payable by a casual dealer under clause (a) of section 15 shall be levied on such part of his sale price which remains after deducting therefrom –

(a) sales of goods declared tax free under section 21;

(b) sales of goods which are shown to the satisfaction of the Commissioner to have taken place in the course of inter-State trade or commerce within the meaning of section 3 of the Central Sales Tax Act, 1956, or in the course of import of the goods into, or export of the goods out of, the territory of India within the meaning of section 5 of that Act.

(2) The tax payable by a casual dealer as referred to in sub-section (1), shall be levied at the rate of tax applicable to a sale of such goods under sub-section (2) of section 16.