with clear explanation

Z O 1) As part of its quality assurance program, the Autolite Battery Company conducts tests on battery life. For a particular D-cell alkaline battery, the mean life is 19 hours. The useful life of the battery follows a normal distribution with a standard deviation of 1.2 hours. Answer the following questions. a. About 68% of the batteries failed between what two values? b. About 95% of the batteries failed between what two values? c. About 99.7% of the batteries failed between what two values