Repeat the step 1 for every bookmark variable that you want to define. Create a field with the volume of a parameter. You can click Write button and use your mouse or writing pad to write the formula here.
Insert a formula in a table cell Select the table cell where you want your result.
On the Table Tools Layout tab in the Data group click Formula. It doesnt important where. Now you can type in and then select a simple equation do not select the equals sign in your Word document and click the Formula button. Click OK to accept the change.