This will bring up the Formula dialog with a default of SUM LEFT. Click the table cell where you want your result to appear. You can create a simple formula to add subtract multiply or divide values in your worksheet.
Click in a cell that should contain the sum of the rows.
In the Formula box check the text between the parentheses to make sure Word includes the cells you want to sum and click OK. You can create formulas in Word to perform simple arithmetic calculations such as addition subtraction multiplication or division. How to add subtract multiply and divide cells in a Word table. Position the cursor where you want to paste a formula.