Welcome to your interview.
The question is on your right: Statistical Significance Testing. 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.
What statistical test would you use to determine whether an observed change is statistically significant, and how would you interpret the result?