treatment of amt charged for cartage in Tax Invoice

Shivam gupta (student) (263 Points)

16 April 2018  
a trader supplies multiple goods taxable at 5% and 12% in single invoice. for supplying goods up-to transporter premise he charges trolly bhaada from customers and adds the same to in the invoice. 

my query is, at what rate the gst shall be levied on such trolly bhaada(cartage) .?
(in light of the fact that all the transport services through road is exempt except GTA, courier...)