貌似有问题...

Here are the last 3 steps you take:

5. leave #2,#3 at x5
6. back and meet #4,#5 at x6
7. all persons arrive B at same time

If you leave #2, #3 at x5 and never pick them up with the car, how can they arrive B at the same time? #2 is slower than #3. Seems by the time you computed, #3 has arrived by walking, #4 and #5 have arrived by car, and #2 is still on the way.

Please check you process...