According to your answer, it looks like you could use some help with basic geometry. We recommend starting with Volume 3 of the Learn Math Fast System. That book starts with pre algebra. Most public schools teach basic geometry through elementary school, but we don't introduce geometry until volume 4, however, you should still start with volume 3, 2, or 1.
RESULTS: 6th Grade Level, however, the Learn Math Fast System is for all ages. Volume 3 covers 6th - 7th grade topics, but there is no mention of grade level within the books.