Vat on lpg

Hello Friends,

What is the correct way of leavying tax on lpg?

a. Whether to levy before subsidy or,

b. after subsidy.

eg:

The basic rate of the cylinder is Rs 1003, rate of tax is 1%,  subsidy given by the Government is Rs 580.

The comsumer rate of lpg is Rs 434 including the commission charged by the distributer.

a. Whether to charge tax on Rs 1003 i.e. Rs10.03  or

b. Rs 423( 1003 - 580)  Rs 4.23

Kindly help in understanding the issue.