Welcome to your interview.
The question is on your right: Moving Average Over Rolling Window. 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.
Given a stream of real-time transaction data, how would you efficiently calculate a moving average of transaction values over a rolling window?