Answer:
(3,4)
Explanation:
The amount of steps applied from the reflection line to the point would be also applied inversely to the image point (after reflection).
From y=x to (4,3), it goes 1 down and also goes 1 right. (NOTE: It does not go down and right. Instead, it goes either down and right)
So now inverse that to make 1 up and also going 1 left.