Which number is missing in the white square?

A man was sitting in his house when he heard a tapping on the door. He went to see who it was. He opened the door and looked around he then heard a tiny voice, "Hey mister, could you lend me 10 bucks?"

The man looked down and saw a snail sitting on his porch. He said, "What do you want?"

The snail said, "Could you lend me 10 bucks?"

The man yelled, "get out of here!" and then kicked him off the porch.

About a year later the man hears a tapping on his door again. He goes out to see who it is. He looks around and he finally heard a tiny voice say, "What did you do that for?"