a) Do we know the total number of days? The point of this question, I think, is that often the expected value is an impossible value, e.g., it's not possible to have 2.5 children. So quite possibly the probability is 0.
b and c) Consult your book for formulas, or look on Wikipedia.
If you have any specific questions, ask away.
Also, please try to pick a more descriptive title (instead of "you") next time.