A university professor believes that some of his students are struggling in the class due to a large amount of assignments in the course. He runs an analysis of all of the classes in the department to determine if there is a relationship between number of assignments in a semester (1, 2, 3, 4, 5, etc., etc.) and final grades (60, 65, 70, 75, 70, etc., etc.). What type of statistical test should be used?