1.6 Students arrive for a lab experiment according to a Poisson process with a rate of 12 students per hour. However, the lab attendant opens the door to the lab when at least four students are waiting at the door. What is the probability that the waiting time of the first student to arrive exceeds 20 min? (By waiting time we mean the time that elapses from when a student arrives until the door is opened by the lab attendant.)