simple distribution

1, In city A, the number of rainstorms can be modelled by a poisson distribution with a mean of 4 rainstorms per year.

Last year, there were more than 4 rainstorms occurred. Estimate how many years after should there be a year with more than 4 rainstorms again. Answer = 3

2, Suppose that the number of misprint on a page of a book of 100 pages follows a poisson distribution with a mean of 0.3 misprint per page.

Let M be the number of pages with misprints. Find the mean and variance of M.
Answer - mean = 25.9, var = 19.2

please list out the steps needed to get to the answers. thanks