For the first part, the question asks you to find the number of students in the UNION of A and B, so you need to add up the number of students that are in both sets.
The second part asks you to interpret what that means: These are the students that use Social Media A, or Social Media B, or both.
The third part ask you to find the number of students in the INTERSECTION of A and B, so you need to look at where the two groups overlap.
The next question asks you to interpret what that means: These are the students that use both Social Media A and Social Media B.
For the last part, you are asked to find the probability that a student is selected at random from the class that uses Social Media A only. To do this, you need to take the ratio of the number of students in Social Media A compared to the total number of students in the entire class, which is 30. (Don’t forget to count the 4 students outside of both circles; they are part of the class, but don’t use either of the social mediums.)