With you are the janitor3, the lab assistant, and the old professor. You've gotten a headstart, but there's only one way to safety: Cross an old rope bridge spanning a massive gorge4. You can dash across in 1 minute, while the lab assistant takes 2 minutes. The janitor is a bit slower and needs 5 minutes, and the professor takes a whole 10 minutes, holding onto the ropes every step of the way. By the professor's calculations, the zombies will catch up to you in just over 17 minutes, so you only have that much time to get everyone across and cut the ropes.