Remember when the result of an equation is a true statement, the solution is "all real numbers". It the result of the equation is a false statement, the solution is "empty set", "null set" or "no solution".
3x + 4 = -2x + 5x + 4
3x + 4 = 3x + 4
This is a true statement, so the solution for x is all real numbers.
In the equation -2x + x - 6 = 6x - 4 - 5x
x - 6 = x - 4
subtract an x from both sides and we have
-6 = 4.
It's obvious that it is a false statement, therefore there is no solution.