researchers for a manufacture of barometer read each of 50 barometers

at the same time of day. the mean of the readings is 30.7 with a standard deviation of 0.28 inch and the readings appear to be normally distributed.
a) what % read over 31.26?
b) what % read less than 30?
c) the company decides to reject barometers that read more than 1.5 standard deviations above or below the mean. What is the critical reading below which the barometers will be rejected?
d) what is the critical reading above which the barometers will be rejected?