Unfortunately this formula would simply add all the numbers to the left of the cell ie. Drag the left side of the formula editor to move it. Place the cursor at the blank cell of the first column then click layout Formula see screenshot.
This will display a Formula Dialog Box which will suggest a default formula which is SUM LEFT in our case.
On the Layout tab in the Data group click the Formula button. If the cell is not empty delete its contents. On the Layout tab under Table Tools click Formula. Position the cursor where you want to paste a formula.