According to your answer, it looks like you could use some help with exponents. We recommend starting with Volume 3 of the Learn Math Fast System. That book will teach you how to work with exponents, plus a whole lot more.
RESULTS: 7th 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.