What activity should you use if you want to calculate a sum into a cell using Excel formulas?

The correct activity to use when you want to calculate a sum into a cell using Excel formulas is the Excel Formula Activity. This activity is specifically designed to write and apply formulas directly into Excel cells, enabling calculations such as summation, averages, and more.

Using the Excel Formula Activity allows you to provide a formula (like SUM) that will execute within Excel, generating the calculated value based on the defined criteria and cell references. This is crucial because it interacts with Excel's formula engine, enabling dynamic calculations that update automatically if the referenced data changes.

In contrast, while writing to a cell through the Excel Write Cell activity can input static values or results, it does not handle the dynamic formula calculations that are necessary for executing operations like summation in real-time. The other options, like reading cells or appending ranges, do not facilitate the placement of formulas into the cell itself, making them unsuitable for this particular task.