If you're good in Math will you help me in this question?

The question is somewhat ambiguous. But if it means that each book "INDIVIDUALLY" can be rounded to 3cm, then each book COULD be at the smallest 2.5 cm each (because 2.5 rounds to 3). Convert 2.5 cm to meters and you get 0.025m per book. Divide 0.8m length by 0.025m length per book, and you get 32 books in total.