SUM for lookup and lookupset report builder 3.0 ssrs

I have a report that should read values from 2 dataset by Currency:

Dataset1: Production Total

Dataset2:Net Total

Ive tried to use Lookup(Fields!Currency_Type.Value, Fields!Currency_Type1.Value,Fields!Gross_Premium_Amount.Value, "DataSet2"), it returns only the first amount from dataset2

Ive tried Lookupset function also but it didnt SUM the retrieved values.

Any one can help please.

Regards