You’re given only a business goal, not a target metric. 1) For each of these goals—Improve Retention, Grow Mobile Usage, and Increase Content Quality—propose a primary metric and 2–3 guardrails each. Make them concrete, time-bounded, and hard to game (avoid vanity metrics). 2) Justify when to prefer rates/percentiles over means and when that choice fails (e.g., freemium/outlier-driven businesses). 3) For a Q&A platform, define a metric suite that captures 'answering quality within 16 hours' without being skewed by late responses; include at least two complementary percentages to capture improvement from 15h to 1h. 4) When the business asks for a long-term effect (e.g., LTV), specify a short-term proxy set and a validation plan to prove the proxy predicts the long-term outcome; outline a backtest that would falsify your proxy choice.