I am taking AP Calculus AB in high school and I am not doing to well. I am using “Calculus - 6th edition” by the publishing company, Houghton Mifflin. The test my teacher gives out come nowhere near the practice problems in my book. I need opinions on what book that has challenging practice problems.

i think i used a steward 4th edition in high school, and it was the same book here @ university for the rest of my calc. very good problems. will check exact edition @ home, as i kept it to help with all these signal processing courses

I need a book in which the difficulty level for the practice problems go from medium to hard, not easy to hard.