car repair shop. repairs are carried sequentially:t(tune-up), an(air-conditioning), b(breaks) with the mean time of 1, 2, 3 hours respectively. assume the repair times ri, i = 1,2,3 are independent and exponentially distributed. what is the probability that 5 hours later the car is in the break repair stage?find p(X(5)=3). Find the exact formula for p(X(5)=3).