621,864
Since the 4 is a smaller digit than a 5, the 6 in the tens place would stay the same while the 4 would become a 0.
All work is shown in picture below.
For this case we have the following system of equations:

Substituting the second equation into the first we have:

The equality is not fulfilled, therefore the system has no solution.
The lines do not intersect.
Answer:
The system has no solution.