According to your answer, it looks like you could use some help with Decimal numbers and Percentages. We recommend starting with Volume 2 of the Learn Math Fast System. You'll learn how to solve percentages in your mind, plus a whole lot more.
RESULTS: 5th Grade Level, however, the Learn Math Fast System is for all ages. Volume 2 covers 4th - 6th grade topics, but there is no mention of grade level within the books.