Standard deviation problem

A little homework help please =/ ... Thank you in advance

The average starting salary for this year's graduates at a large university is $20,000 with a standarad deviation of $8,000. Furthermore, it is known that the starting salaries are normally ditributed.

a. What is the probability that a randomly selected LU graduate will have a starting salary of at least 30,400?

b. Individuals with starting salaries of less than $15,600 receive a low income tax break. What percentage of the graduate will receive tax break?

c. What are the minimum and the maximum starting salaries of the middle 95% of the LU graduates?

d. If 189 of the recent graduates have salaries of at least $32,240, how many students graduate this year from the university?