a. A company produces lightbulbs whose life follows a normal distribution, with mean 1200 hours and standard deviation 250 hours. If we choose a lightbulb at random, what is the probability that its lifetime will be between 900 and 1300 hours? (answer in three decimal places)

b. An instructor has found that the time spent by students on a particular homework assignment follows a normal distribution with mean 150 minutes and standard deviation 40 minutes. The probability is 0.8 that a randomly chosen student spends less than how many minutes on this assignment. (answer in one decimal place)