Answer
We can represent the number of the page facing the left-hand page of this book as:
$$x + 1$$
Work Step by Step
We know that if the number on the left-hand page of this book is $x$, then we know that the page facing this one will have a number that will be one more than this page.
We can represent the number of the page facing the left-hand page of this book as:
$$x + 1$$
