Your question is Optimize Slow Spark Jobs. 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).
Tell me about how you would resolve a situation where a Spark job takes too long to execute, and how you would use Spark UI to diagnose it.
Explain a practical, systematic investigation from job symptoms through remediation. Cover how you distinguish input, CPU, memory, shuffle, skew, serialization, and cluster-resource problems, and how you validate that an optimization improved runtime without changing results.