standard deviation problem.

Consider a sample size of 100 with a standard deviation of 10.
a) What is the probability that the sample mean will be within 1 of the value of "u"?
b) Approximately 95% of the time, the mean will be within ___________ of "u"?
c) Approximately 0.3% of the time, the mean will be farther than ___________ from "u"?

I am really lost with this problem so please show me a step-by-step way of solving it.
Thanks.