The correct answer is B. 3:25 p.m.
If Seth needs to arrive at tryouts at 3:30 p.m., he needs to leave enough time to walk home, eat his snack, and walk back to school. Given that it takes him a total of 40 minutes to walk to and from school and eat his snack, he needs to leave school at:
3:30 p.m. - 40 minutes = 2:50 p.m.
However, we also know that it takes him 15 minutes to walk to school from home. Therefore, he needs to start walking from home 15 minutes before 2:50 p.m., or:
2:50 p.m. - 15 minutes = 2:35 p.m.
Finally, we know that he takes 15 minutes to walk from school to home, so he will arrive at home at:
2:35 p.m. + 15 minutes = 2:50 p.m.
Therefore, he needs to eat his snack until:
2:50 p.m. + 10 minutes = 3:00 p.m.
And he needs to start walking back to school at:
3:00 p.m.
It will take him another 15 minutes to walk back to school, so he will arrive at:
3:00 p.m. + 15 minutes = 3:15 p.m.
Adding the time he needs to eat his snack to the time it will take him to walk back to school, he will arrive in time for tryouts at:
3:15 p.m. + 15 minutes = 3:30 p.m.
Therefore, Seth needs to leave school by 3:25 p.m.