There is not possible solution in the real number system or the complex field.
Oddly, before I answer your question, I would point out that the equation given is a perfectly legitimate equation in some computer languages. It has the meaning of
Take the current value in memory location x
Subtract 5 from it.
Put the new result in memory location x.
But that is not what you are being asked about.
The blank you could put in 4
so 4 = 4 - 5
4 = - 1
The second blank will give you the result of 4 = - 1 which can't be true in a million years.
