2x = x + 3
Subtract 'x' from both sides of the equation:
2x - x = x + 3 - x
x = 3
You can check this is true by putting the value x = 3 into the original equation:
2x = x + 3
2(3) = 3 + 3
6 = 6
So both the left and right hand sides of the equation equal the same thing, so the solution x = 3 is correct.