On a street AB, three traffic lights are connected. Let i be the index of the ith traffic light and Ti is the waiting time behind the ith traffic light. On average, the waiting time for the ith traffic light is i minutes, a) What is the appropriate probability distribution to model Ti? (5) b) Find the probability that T1 is greater than 30 seconds. (5) c) What is probability model of T1 +T2, if waiting times are independent. (specify the parameters of the model) (5) d) What is the expectation and standard deviation of the waiting time on the street AB?