Machine A takes 10 hours to complete a task. Machine B takes X hours. How many hours will it take for Machines A and B to complete the task together?

✓ Correct Answer: Option D

From (1), Machine B takes 10+5=15 hours. A's rate is 1/10, B's is 1/15. Combined rate = 1/10+1/15 = 5/30 = 1/6. Time = 6 hours. Sufficient. From (2), 75% of task in 4.5 hours means full task in 4.5/0.75 = 6 hours. This is the combined time. Sufficient.