This is a poorly described problem because books are different lengths meaning they possess different number of pages.
With that being said let's assume all books have exactly the same number of pages.
The formula to calculate how many books can he read in 12 days it's obvious: [tex]\frac{3}{4}\times12[/tex] which is [tex]\frac{3\times12}{4}[/tex] and then [tex]\frac{36}{4}=\boxed{9}[/tex]. Hope this helps!
