Try this explanation:
A: The property of intersection point is: on the graphs it belongs to the first line and to the second line, in another word, it belongs to the both lines. 'To the both lines; means, for the both equations, this value of 'x' converts the left side and the right side to the same value (one value 'x' ⇒ one value on the left part and the same value on the right part of the equation 4-x=2x+3).
B: see the attachment, based on 4 steps.
C: see the attached graph. The intersection point is marked with green colour.