Section 7(8)(b) in Bihar Motor Vehicles Taxation Act, 1994
(b)A one time tax of Rs. 4,000.00 shall be payable by all trailers up to 3,000 kgs. registered laderi weight and Rs. 6,000.00 shall be payable by all trailers more than 3,000 kgs registered laden weight used or kept for use alongwith tractors for other than agricultural purpose: