Question28:

 what will be rate of GST on sale of old car ?

Answer:

Notification No. 09/2018 -Integrated Tax (Rate) dt. 25th January, 2018, reduce rate from 28% to 18%/12% on old and used motor vehicles  on the basis of engine capacity and length of motor vehicles under HSN 8703 /87 and  Vide Notification No. 1/2018-Compensation Cess (Rate)  dt. 25th January, 2018 , compensation cess on all old and used motor vehicles shall be NIL w.e.f 25.01.2018 

The rate(18% /12%) on sale of old car in your case depends upon car  engine capacity, length of motor vehicles or diesel or petrol vehicle. So refer the attached above said notification.
The benefit  of this notification is available only when ITC has not taken.

Value for the purpose of this notification is as follows:-

Value of supply (where dep claimed u/s 32) = Consideration received for sale of old vehicle- Depreciated value on the date of supply

If value calculated above is negative then it shall be ignored means No tax

Value of supply (any other case) =  selling Price- purchase price 

If value calculated above is negative then it shall be ignored means No tax 

The copy of  above said notification are enclosed herewith for your reference

(Reply dt. 26/3/2018)