Bill wrote down on a piece of paper the equation below, and told Art to fill in the blanks only using each of the digits 1-6 only once, to make a valid equation.

"Easy enough," said Art, picking up a pencil. After a few minutes of wracking his head, however, he was sure Bill had had a few too many. Bill insisted he hadn't, and there is actually more than one way to do it, to which Art threw up his hands in defeat.

*How many ways can you find to fill in this equation using the digits one through six, once each?*

___ + ___ = ___