Need help with solving accounting problem

A group of students took a test. Below are the summary of grades and where the students sat in the classroom. Find the probabilities below and write the answer as a fraction. a. If one student is chosen at random, find the probability that the student passed the test. b. If one student is chosen at random, find the probability that the student did not pass the test OR sat in the middle of the classroom. c. To the best of your ability, explain your calculations to the parts (a) and (b)