Welcome to your interview.
The question is on your right: Moving Average With Window Functions. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
Use window functions to calculate the moving average of user session lengths over the last 30 days.