GST RATES PACKING

Pl clarify the issue
work order given to pack sugar owned by sugar factory in half kg packets using film owned by job worker @ Rs.2300/mt of sugar.
job worker is packing the sugar owned by the sugar factory with his own film and labour and submitting the bills as follows :
Bill no.1- film charges (HSN code 3920) @ Rs.1100/mt @ 18% GST ie Rs.1298/mt
Bill no.2 - packing job work charges (HSN code 9988) @ Rs.954.28/MT @ GST 5% ie Rs.1002.
I want to know the correctness of above billing process on the rates of 18% and 5% and also applicability of HSN codes . what are the provisions of GST on job work involving material of job worker