The output from a sewage treatment plant is constantly monitored to assess treatment efficacy. Suppose that the mean coliform content is 20 bacteria / ml with a standard deviation of 4 bacteria / ml. Assume the distribution of coliform content is approximately normal. An automatic measuring device is being used to monitor the bacterial levels. An alarm should ring whenever the bacterial level exceeds the 97.5th percentile. When should the alarm ring?
a. 20 bacteria per ml
b. 32 bacteria per ml
c. 24 bacteria per ml
d. 28 bacteria per ml
e. 16 bacteria per ml