You can add Formulas to Tables in Microsoft Word with relative ease. To learn how to insert Formula in Word Table, read this article.

To create a formula, click inside the cell where you want the product to appear and go to the "Layout" tab of the Word Ribbon. Click the "Formula" icon and enter "=PRODUCT" in the "Formula" field.

Review the Formula Format table in the graphic below for the correct commands that tell Word which direction to calculate (these go inside the parentheses).