Can you solve the bridge riddle?

Do you like riddles?

If yes, then try solving the bridge riddle. What it will be about:

Taking that trainship in a remote mountain lab might not have been the brightest idea. Pulling that lever with a skull symbol just out of curiosity probably wasn’t so smart, too. But now it is not time for regrets because you need to get away from these mutant zombies...ASAP. You should use math to get you and your friends over the bridge before the zombies arrive!