The petitioner is a partnership firm having its place of business at Calcutta. The petitioner undertakes execution of contracts for supply, erection and commissioning of electrical equipments in different States. On 7.2.86, it entered into an agreement with the Executive Engineer, Micro Hyde! Investigation Division, Government of Tripura for execution of the work of "supply, erection and commissioning of 66/11 K.V.6.3 MVA Sub-Station at Sonamura in the State of Tripura". The work also involved supply of materials required for the purpose. The petitioner purchased the materials in deferent States outside the State of Tripara or placed orders for supply of the same to Tripura for use in execution of the aforesaid contract. The terms of the contract stipulated movement of the goods from such other States to the State of Tripura. As the transactions in this case related to a period after the coming into force of the Constitution (46th Amendment )Act, 1982 which enables the States to levy tax on the transfer of property in goods involved in execution of works contract and incorporation of section 3A in the Tripura Sales Tax Act, 1976, hereinafter '-the Tripura Act", by