how to add a null value in a datagrid cell to an integer value in another cell in the same datagrid

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VB

Hi all,

can someone point the way on one this. I have a datagrid and am trying to sum up all the values in column3 together, some cells in that column have null values while others have integer values as you can see below. Like below the cell under column 3 under the value 400 and adjacent to colour blue and the material cotton are empty (null) values and this goes on down the row so how can i sum the entire cells in the column together.

Column1 Column2 Column3 Column4

- 1 blouse 400 0 ----------(node or parent node)
Blue 1 --------(Sub node or child row)
Cotton 1 --------(Sub node or child row)

- 3 Camisole 350 0 ----------(node or parent node)
White 2 --------(Sub node or child row)
Linen 2 --------(Sub node or child row)
Press Only 175 2 --------(Sub node or child row)

- 2 Dress 250 0 ----------(node or parent node)
Yellow 3 --------(Sub node or child row)
Wool 3 --------(Sub node or child row)
Press Only -125 3 --------(Sub node or child row)

- 2 Shorts 450 0 ----------(node or parent node)
Yellow 4 --------(Sub node or child row)
Wool 4 --------(Sub node or child row)
Press Only -225 4 --------(Sub node or child row)

regards

ade