transactions +----------+--------+------------+---------+-----------+ | user_id | txn_id | txn_date | amount | is_fraud | +----------+--------+------------+---------+-----------+ | 101 | 9001 | 2024-04-01 | 13.99 | 0 | | 102 | 9002 | 2024-04-02 | 7.99 | 1 | | 101 | 9003 | 2024-04-03 | 15.49 | 0 | | 103 | 9004 | 2024-04-05 | 11.99 | 0 | | 102 | 9005 | 2024-04-06 | 8.49 | 1 | +----------+--------+------------+---------+-----------+ ##### Scenario Analyst is provided with transaction logs and must write SQL and lightweight Python to build retention metrics. ##### Question Write a SQL query that returns, for each user, the first transaction date and the number of transactions made within 7 days of that first purchase. Write a SQL query that computes overall Day-7 retention rate. Given a Python list of n integers, write a function that returns the two numbers whose sum is closest to zero (assume at least two numbers). ##### Hints Use window functions for datediff; in Python aim for O(n log n) or better.