Ah ha! I got it after trying for some time... It's 78!
Flip your monitor upside down. What pattern do you see now? When you orient the numbers in the correct position, this is what you see...
The numbers are going in ascending by one each time. The ? is clearly 87. Let's flip this number back around to see what it looks like. Flip the order to make the number look like it would in the sequence. You get 78!