Explanation:
The trains are going in opposite directions.
For every 1 hour,
The trains are 75 + 63 = 138 miles further apart.
Number of hours to be 621 miles apart
= 621/138 = 4.5 hours.
4.5 hours after 1 p.m. => 5:30 p.m. (B)
4.5m questions
5.7m answers