If you're reflecting it about the x-axis, its x-ordinate doesn't change. This works best when you visualise what is happening with the reflection.
As we reflect it about the x-axis, we are essentially 'folding' the grid with the crease mark being the x-axis. Thus, we know that the x-ordinate will not be affected. Also, the y-ordinate will be the same magnitude from the x-axis, just in opposite signs, because no transformation occurs.
Thus, the reflected coordinates become: (4, 3)