How to do summation of row values, if one of the row has same value

We can do it with the help of a group by

A LINQ approach could start by:

Assign activity:
LHS: dtResult | Datatype: DataTable
RHS: dtData.Clone - dtData is your DataTableVar

Assign Activity
LHS: dtResult
RHS

(From d in dtData.AsEnumerable
Group d by k=d("Material ID").toString.Trim into grp=Group
let s = grp.Sum(Function (x) CDbl(x("RECEIVED QUANTITY").toString.Trim))
let ra = new Object(){grp.First()(0),grp.First()(1),s,grp.First()(3),grp.First()(4)}
Select r=dtResult.Rows.Add(ra)).CopyToDataTable

It can be the case that the CDbl /Double Conversion is to adopt /to finetune. Also, depending on the dataquality some data cleansing can enhance the process