Your question is Estimate Sample Size for Engagement Test. 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).
You work on a ride-sharing marketplace and want to test a change to the rider app that is expected to increase engagement. You need to estimate how much traffic the experiment should run on before you launch.
How would you estimate the sample size needed for this experiment on user engagement, and what assumptions would you make before running it?