lifetime of a washing machine

1.The lifetime of a certain manufacturer’s washing machine is normally distributed with mean 4 years. Only 15% of all these washing machines last at least 5 years. What is the standard deviation of the lifetime of a washing machine made by this manufacturer? 2. You have been told that the distribution of regular unleaded gasoline prices over all gas stations in Indiana is normally distributed with mean $2.95 and standard deviation $0.075, and you have been asked to find two dollar values such that 95% of all gas stations charge somewhere between these two values. Why is each of the following an acceptable answer: between $2.776 and $3.081, or between $2.803 and $3.097? Can you find any other acceptable answers? Which of the many possible answers would you give if you are asked to obtain the shortest interval