Calculation of Money/Currency Field

I need to fetch all related quote products under the quote entity. I used a query expression for this to retrieve the corresponding Total amount for each product. Now I need to sum the total amounts. My code is not working, the field I’m retrieving is a money/currency field.

My code goes like this:

                        Guid RecordGuid = entity.GetAttributeValue<Guid>("quoteid");

                        QueryExpression query = new QueryExpression("quotedetail");

                        query.ColumnSet = new ColumnSet(new string[] { "nexus_marginalamount", "baseamount"});

                        query.Criteria.AddCondition("quoteid", ConditionOperator.Equal, RecordGuid);

                        query.PageInfo.ReturnTotalRecordCount = true;

                        EntityCollection result = service.RetrieveMultiple(query);

                        Money  m = new Money ();

                        foreach (Entity EntityResult in result.Entities)

                        {

                           m = m + EntityResult.GetAttributeValue<Money>("nexus_marginalamount");

                        }

                        entity["nexus_marginalamount"] = new Money(m.Value);