Please Please Help Me with this Statistics Problem!

In a study of anorexia treatments, 29 young women received counseling for a 3 month period and their weight was measured at the end of the period. The average woman gained 3.1 pounds and the standard deviation was 7.31.
a. What is the estimated standard error of this sample?
b. If the treatment was actually ineffective and should have a mean change of 0, what is the probability that our sample would have a mean gain of 3.1 pounds?
c. How would your answer to Part B be different if you were to use the students t distribution instead and a two tailed 95% confidence interval?

The link below is to about 15 Khan Academy videos on statistics. They are free and you can watch as many times as you want.

https://www.khanacademy.org/search?page_search_query=statistics