4. (5 points) A total of 4 buses carrying 150 students from the same school arrives at a football stadium. The buses carry, respectively, 40, 35, 25, and 50 students.

One of the students is randomly selected. Let X denote the number of students that were on the bus carrying this randomly selected student. One of the 4 bus drivers is also randomly selected. Let Y denote the number of students on her bus. Calculate E[X], var[X], E[Y], and var[Y]