Answer:
9 pm
Explanation:
A pulls into the station every 6 hours while B pulls into the station every 3 hours. Hence, for every time A pulls up, B must have pulled up twice.
They both pulled into the station at 3 pm. At 6 pm (3 pm + 3 hours), B would pull into the station while A would still be on the road. At 9 pm (3 pm + 6 hours), B will pull in once more while A will just be pulling up the first time since 3 pm.
Hence, the next time both trains will pull into the station at the same time would be 9 pm.
