Susan has just completed her second semester in college. She earned a grade of Upper D in her 1-hour linear algebra course, a grade of Upper D in her 4-hour economics course, a grade of Upper C in her 2-hour biology course, and a grade of Upper A in her 3-hour creative writing course. Assuming that A equals 4 points, B equals 3 points, C equals 2 points, D equals 1 point, and F is worth no points, determine Susan's grade-point average for the semester.