Your question is Determine A/B Test Sample Size. 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 do you determine the required sample size for an A/B test?
Explain the inputs and assumptions you need, including baseline metric rate, minimum detectable effect, significance level, and statistical power. Show the calculation for a binary primary metric, explain how traffic and test duration follow from the result, and describe checks you would make before trusting the estimate.