Answer:
11.18% probability that the city's weather station records exactly 4 snowstorms with at least 12 inches of total snow accumulation for one randomly selected year in the period.
Step-by-step explanation:
In a Poisson distribution, the probability that X represents the number of successes of a random variable is given by the following formula:

In which
x is the number of sucesses
e = 2.71828 is the Euler number
is the mean in the given time interval.
78 snowstorms with at least 12 inches of total snow accumulation.
This means that 
Find the probability that the city's weather station records exactly 4 snowstorms with at least 12 inches of total snow accumulation for one randomly selected year in the period.
This is P(X = 4). So


11.18% probability that the city's weather station records exactly 4 snowstorms with at least 12 inches of total snow accumulation for one randomly selected year in the period.