View Formulas in a Table in Word. In older versions of Word this appears as the Layout. Design and Layout.
On the Layout tab under Table Tools click Formula.
Click the table cell where you want your result to appear. Click in a cell that should contain the sum of the rows. Now go to the first row last column and choose Table Tools Layout Formula. In the Formula box check the text between the parentheses to make sure Word includes the cells you want to sum and click OK.