7 leaves fell in the first hour.
4 leaves fell in the second hour.
4 leaves fell in the third hour.
The total number of leaves that fell during the 3 hours is 7 + 4 + 4 = <<7+4+4=15>>15 leaves.
The average number of leaves that fell per hour is 15 leaves / 3 hours = <<15/3=5>>5 leaves per hour.
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