The average starting salary of this year's graduates of a large university (LU) is 20,000 with a ...

The average starting salary of this year's graduates of a large university (LU) is 20,000 with a standard deviation of 8,000 . Furthermore, it is known that the starting salaries are normally distributed.
 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 graduates will receive the 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 graduated this year from this university?