Grace should use the SUM function in order to add the values from a list of regional sales data.
SUM
Step-by-step explanation:
The average function would have returned the average of the list of regional sales data. The average is calculated by dividing the sum of all entries by the total number of entries.
The maximum function would have returned the maximum value from the list of regional sales data.
The IF function is used to return a result based on some comparison. Grace cannot use IF function as she is not making any decision based on some comparison.