The finance director wants to see users whose net revenue is at least 100 — i.e. the sum of purchases minus refunds per user lands at 100 or higher. For each user compute the net revenue (purchase events count positively, refund events count negatively; refund amounts are already stored with a negative sign in the data) and keep only those whose net revenue is at least 100. Return the user id and their net revenue, ordered by revenue descending.