Probability of Outdoor Activities Exceeding 18 Days

In a certain city, the local government is trying to analyze the relationship between the amount of rainfall and the number of days people choose to go out for outdoor activities. A study found that over a period of one year, the average daily rainfall was 2 inches, with a standard deviation of 1 inch. During the same period, the average number of days with outdoor activities was 15 per month, with a standard deviation of 3 days.

If the government assumes the number of outdoor activity days follows a normal distribution, what is the probability that in a given month, the number of days for outdoor activities is more than 18?

Use the Z-score formula $$Z = \frac{X - \mu}{\sigma}$$, where $\mu$ is the mean and $\sigma$ is the standard deviation for the respective distribution.