Left page numbers are always even and right page will have a number 1 greater that the left. so its not possible to have a sum of 87.
If even page is 2n then right page = 2n + 1:-
2n + 2n + 1 = 87
4n = 86
n = 86 / 4 = 21.5 and 2n = 43 but left page is even so its not possible to have a sum of left + right = 87.
