The next task that Gruber has them do is to reach a pay phone. He then gives them a riddle and has them call back within 30 seconds to the right phone number (the answer to the riddle is the last four digits) or else the trash can full of explosives will be detonated. They call back with the right phone number but it is past 30 seconds. Carver and McClane duck out of the way as Gruber laughs.