if the shape is a square, then all sides must be the same so the top and bottom would just be 2s, which would be equal to 12 and divide that by 2 to get your answer of what s is.
Let the total amount of pages be t t=30+1/8t+2/8t now simplify t=30+3/8t 5/8t=30 divide 30 by 5 1/8=6 now you know 1/8 of the book is 6 pages which means the whole book has 48 pages.
. (Integration along the 
axis would be way easier, but whatever)