請教pjiang 老師及小白兔姐姐等大俠，incorrect fee 140

My I-140 reached USCIS on July 27, 2007, but rejected. I got I-797,
Notice of Action ----------. The application or petition cannot be accepted because the proper fee of $475.00 U. S. is not attached. Since ………. What should I do next?
Many thanks!