A sociologist will conduct a two-sample tt-test for a difference in means to investigate whether there is a significant difference, on average, between the salaries of people with bachelorâs degrees and people with masterâs degrees. From a random sample of 32 people with a bachelorâs degree, the average salary was $55,000 with standard deviation $3,500. From a random sample of 28 people with a masterâs degree, the average salary was $58,000 with a standard deviation of $4,000. With a null hypothesis of no difference in the means, what is the test statistic for the appropriate test to investigate whether there is a difference in population means (masterâs degree minus bachelorâs degree)?