Refund for inverted duty structure

for purchase of materials with GST 5%,18% and 28% which together processed will give the output material sold at GST 5%. In this case, how will I find out the turnover not covered under inverted duty structure for calculating total turnover used in the formula:
[Net ITC * ( total turnover/aggregate turnover)]- output tax payable
where : total turnover =turnover for the period- turnover not covered under inverted duty structure.

Kindly help me with ur valuable inputs.