Help with LINQ groyuping by multiple columns

[wiss.dev]

Hi,, need some guidance in vb.net linq
i have a data table with the following columns

ItemCode, ItemDescription,Height,Width,Quantity, Price

need to group rows by Description, height and width and sum the quantity

attempted this

Dim q = From tbl In ocom.ds.Tables("table").AsEnumerable()
        '        Group tbl By tbl.Field(Of String)("ItemDescription"), tbl.Field(Of Decimal)("w"), tbl.Field(Of Decimal)("H") Into Comps()