A submarine has three navigational devices but can remain at sea if at least two are working. suppose that the failure times are exponential with means 1 year, 1.5 years, and 3 years. formulate a markov chain with states 0 = all parts working, 1 = part 1 failed, 2 = part 2 failed, 3 = part 3 failed, 4 = two parts failed. compute e0[v4] (the expected hitting time of state 4 starting from state 0) to determine the average length of time the boat can remain at sea.