The two facing pages are consecutive pages.
Let the first page of the two be x
Let the next page be x + 1
The product of the two facing pages is 306:
(x) (x + 1) = 306
x² + x = 306
Write as quadratic equation ax² + bx + c =0:
x² + x - 306 = 0
Solve by quadratic formula or factoring.
By factoring:
(x - 17) (x + 18) = 0
x - 17 - 0 x + 18 = 0
x = 17 x = -18
Choose the positive root (solution), x = 17
The pages are 17 and 18.