Calculate DataGridView Cells value by Columns dynamically

I have a datagridview in the following shape:

Name    0.5 Litre     1 Litre         1.5 Litre

A          25               30                 33

B          20               25                 28

C          31               36                 39

D          29               34                 37

Now I would like to add a row in the last and calculate dynamically the value of each column like this:

Name    0.5 Litre     1 Litre         1.5 Litre

A          25               30                 33

B          20               25                 28

C          31               36                 39

D          29               34                 37

Total:   105              125              137

How can I do it?