Four buses carrying 157157 high school students arrive to montreal. the buses carry, respectively, 3636, 4545, 3030, and 4646 students. one of the studetns is randomly selected. let xx denote the number of students that were on the bus carrying this randomly selected student. one of the 44 bus drivers is also randomly selected. let yy denote the number of students on his bus. compute the expectations and variances of xx and yy: