Answer:
5x
Step-by-step explanation:
If the blank were to be occupied with 5x there would be no solutions
Observe...
5x - 8 = 5x + 2
* subtract 5x from each side *
5x - 5x cancels out
5x - 5x cancels out
we're left with -8 = 2
which is not true
Hence if the blank = 5x the equation will have no solution
