I don't want to seem stupid, but there's nothing obvious to me here. The only thing that remotely makes sense is the following:
On the straight line ADE, AD is congruent to DE. On the straight line FDB, FD is congruent to DB. Prove that triangles ADF and EDB are congruent. (Which they are: two sides and included angle, the angles ADF and BDE being equal because they are vertically opposite.)
But this is rather a guessing game, don't you think?