Basically you need a groupBy column D and sum values of O..better read all the data into datatable and then use dt = dt.AsEnumerable.GroupBy(function(x) x("ColumnD").ToString).Select(function(x) dt.Loaddatarow({x.First()("ColumnA").ToString,similrly include all columns,x.Sum(function(y) Cdbl(y("ColumnO").ToString)).ToString,other columns if present},False)).CopyToDataTable
Bow you can clear the sheet or write the data dt to new sheet