Your question is Evaluate Marketing Campaign Efficiency. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
How would you evaluate whether a marketing campaign is efficient? Explain which primary and guardrail metrics you would select, how you would calculate them, and how you would distinguish incremental impact from conversions that would have occurred anyway. Describe how you would segment results and what evidence would support scaling, optimizing, or stopping the campaign.