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

The most appropriate activity for calculating a sum into a cell using Excel formulas is the one designed specifically for writing formulas directly into Excel cells.

When you want to derive a value by using a formula within an Excel spreadsheet, the activity responsible for this is intended to accept a formula string and place it into a specified cell. This allows Excel to process the formula correctly, applying its inherent functions such as SUM to compute the result based on the specified cell references and values.

While other options may seem relevant, they either do not pertain to writing formulas or don't accurately describe the functionality required for placing a formula into an Excel cell. For example, simply writing to a cell without the implication of processing a formula would not yield the desired summation outcome; it would treat the data as static text or numbers. Therefore, using the correct activity ensures that Excel interprets the entry as a formula and performs the calculation as intended.