I think that the product of the two facing pages of the book is only 156.
If we work with the 156156 we dont get integer numbers as a solution to the problem, as it should be.
So if the P is for the one page the next facing page is P + 1 then we will have P(P+1) = 156
so P2 + P - 156 = 0 we get P = 12 (the second negative solution is rejected) the next page will be P+1 = 13
chck; 12 x 13 = 156