A small hotel exported its March bookings to bookings.csv and its room list to rooms.json. The setup cell loads the bookings as a list of dictionaries; every value is still text.
The tasks mix the whole unit: converting text to numbers and dates, filtering rows, counting with Counter, grouping with defaultdict, sorting by two keys, joining the JSON room types, and writing a file.
Each answer is also checked on a hidden April export with different guests and amounts, so build every result from the data rather than from what you see on screen.