Depending on the equation there can be three possible cases:
1- There can be 1 specific solution for the variable:
2x+4= 3
where x= -1/2
2- there can be an infinite amount of solutions:
2x+x-2=3x-3+1
where x=x
3- there can be no answer:
3+2x-x=5-3x+4x
where the solution doesn't exist