Question 4: (20 points) My home uses two light bulbs. On average, a light bulb lasts for 100 days (exponentially distributed). When a light bulb burns out, it takes an average of 10 days (exponentially distributed) before I replace the bulb. - Formulate a three-state birthdeath model of this situation. 0 Determine the fraction of the time that both light bulbs are working. 0 Determine the fraction of the time that no light bulbs are working