The numbers are part of an arithmetic progression, where the difference between each succeeding number is reduced by 1 each time. Between 107 and 98, the difference is 9. Between 98 and 90, the difference is 8, and so on. This is shown below:
107 - 98 = 9
98 - 90 = 8
90 - 83 = 7
83 - 77 = 6
77 - x = 5
x - 68 = 4
68 - 65 = 3
From that, we can solve for x using either of the equations:
77 - x = 5
x = 77 - 5
x = 72
Therefore 72 would complete the pattern.