Corner Store Co. logs each day's takings and wants a running total per store — the revenue so far, growing row by row.
daily
A store can post two rows on the same day (two takings entries). The running total should step through them one row at a time, so within that day the total climbs with each row.
Your task: for each row return store, day, amount, and a running_total — the cumulative sum of amount within that store, ordered by day, adding one row at a time up to and including the current row.
Assign your answer DataFrame to result. Row order doesn't matter.