# Puzzle on a blackboard [closed]

What is the missing number in the picture above?(question is from some puzzle game) I tried some approaches, but haven't found any meaningful rule..thanks in advance!

## closed as off-topic by Deusovi♦Jun 30 at 0:49

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This looks like a puzzle you found elsewhere. For content you did not create yourself, proper attribution is required. If you have permission to repost this, please edit to include (at minimum) where it came from, then vote to reopen. Posts which use someone else's content without attribution are generally deleted." – Deusovi
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• Welcome to Puzzling! What puzzle game is this from? If a question is taken from somewhere else, you need to specify where exactly it's from. – Deusovi Jun 30 at 0:50

$$\frac{\frac{(x-9)\cdot 5}2-4+12}3+7=x$$
$$\frac56x+\frac{13}6=x$$
$$x=13.$$