Assuming the student completes at least 85% of the work in the textbook, including the paper assignments and the essay requirement, this course is worth 2 years' credit. This course satisfies 1 year's worth of credit for both composition and American Literature. If the student would only like one year's worth of credit for the course, completing 65% of the text and questons would easily suffice for one year American Literature credit.
As the teacher, you may decide which literary works to include in the 85% or 65% figures mentioned above. The best approach for that would be to include works and assignments from each time period covered in the text.