A sociologist studying teen behavior took independent random samples of students from two high schools, f and g. Of the 80 students selected from high school f, 36 indicated they had seen a certain movie. Of the 72 students selected from high school g, 18 indicated they had seen the movie. Which of the following is the test statistic for the appropriate test to investigate whether there is a difference in population proportions (high school f minus high school g) ?.