help me with this statistics problem

In some mining operations, a byproduct of the processing is mildly radioactive. Of prime concern is the possibility that release of these byproducts into the environment may contaminate the freshwater supply. There are strict regulations for the maximum allowable radioactivity in supplies of drinking water, namely an average of 5 picocuries per liter (pCi/L) or less. However, it is well known that even safe water has occasional hot spots that eventually get diluted, so samples of water are assumed safe unless there is evidence to the contrary. A random sample of 35 specimens of water from a city's water supply gave a mean of 5.27 pCi/L and a standard deviation of 0.87 pCi/L. a) Is there evidence to conclude that the water is unsafe (4-step process)? b) Interpret what your p-value (from a) means in real world terms