Can you solve it? 
If you need a hint, try approaching it form a different angle! Give up? Then read on!
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So this problem requires a bit of different thinking. If you're like me, you were looking for a pattern when you just started looking, but there is just no patten that works out just right. So what's the solution?

Well if you actually look at the puzzle upside-down, you'll see that a switch in perspective is actually all you needed - and the solution is actually 87. So how quick did you solve it? Did it take you a lot of time like me, or do you actually have a much younger mind than people would think?