price cum duty means the price is inclusive of the duty element
like in the above example suppose the cost of goods is rs108 price cum duty that means it includes excise duty in rs108
so to find the price you assume if price is 100 and duty rate is 8%then total cost would be rs108.so if the price cum duty in the problem say is 216 then what is price.
IE RS 200 then duty would be 16
for example if the price cum duty is 108 and excise duty rate is 8% then divide 108/108 multiply with 100