Can someone explain how to solve?

The amounts of nicotine in a certain brand of cigarette are normally distributed with a mean of 0.935 g and a standard deviation of 0.326 g. The company that produces these cigarettes claims that it has now reduced the amount of nicotine. The supporting evidence consists of a sample of 50 cigarettes with a mean nicotine amount of 0.861 g. Assuming that the given mean and standard deviation have NOT changed, find the probability of randomly selecting 50 cigarettes with a mean of 0.861 g or less. P0?