Three high schools participated in a study to evaluate the effectiveness of a new computerbased mathematics currk'ulum. In each school, four 24-student sections of freshman algebra were available f9r the study. The two types of instruction (standard c'Urriculum, computerbased curricUlum) were randomly assigned to the four sections in each of the three schools. At the end of the term, a standard mathematics achievement test was given to each of the 24 students in each section. a. Is this study experimental, observational, or mixed experimental and observational? Why? b. Identify all factors, factor levels, and factor-level combinations. c. What type of study design is being implemented here? d. What is the basic unit of study?