I need help to solve these exercises step by step with the procedure, thank you very much.

2. Assuming that the survival time, in years, of patients who undergo a certain surgical intervention in a hospital follows a Gamma distribution with parameters a=0.81 B =7.81. Calculate: a. The probability that the patient will survive up to 8 years. b. The probability that the patient will live between 15 to 20 years. C. The probability that the patient will live more than 20 years.

4. Suppose that telephone calls arriving at a particular switch follow an exponential distribution with an average of 5 calls per minute. What is the probability that more than 5 calls will arrive at the switch? What is the probability that 5 to 10 calls will arrive on it