Your question is Flight Booking System Design. 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).
Design a flight booking system.
Clarify the scope, then explain how you would use machine learning to retrieve and rank flight offers while preserving accurate availability, pricing, and booking correctness. Cover the online request path, offline training path, latency and scale assumptions, evaluation, monitoring, and failure handling. Distinguish recommendation quality from transactional booking guarantees.