Issue of "c" form

What would be the value of 'C' forms and how the purchasing dealer will issue the 'C' forms under the following circumstances :

1. 'X' makes an inter state sales to 'Y' for say Rs. 100000/- in the month of January 2014 and 'Y' makes sales return of the same invoice for some materials for Rs. 35000/- against credit Note in the month of say February 2014. While issuing the 'C' Form, on what value will be issue the 'C' Form by Y to X

2. In the above circumstance if sales return will made in other quarter.