Now in the formula bar type "=" then select the cell in column A which will enter the cell reference after the "=". Now type "+" after the cell reference, and now select the correct cell in colum B (which will enter the cell reference into the formula).
Now click on the gree tick in the green tick in the formula bar and the total should appear in the first cell in column C.
Select the cell that we have just entered the formula in and right click. From the menu select copy.
Select the range of column C that you want the totals, right click and select paste and you are done.