How to the reflection of a point about a line?

Question

I've been doing some problems on the topic Reflection.And struggling with it when I am doing it graphically. I have solved it using Reflection Matrix but graphically it is giving the wrong answer. Please enlighten me where I am wrong?

I solved it for the equation Y = X correctly like

I have to find the reflection of the point (2,5) about Y = X, whose answer will definitely be (5,2)

HOW I DID IT.

First of All I find the corresponding point on the line Y = x, which will be (5,5) and (2,2), and the corresponding reflected point will have the same value of x coordinate as (5,5) and same value of Y coordinate as (2,2) so the answer will be (5,2) which is correct.

I am attaching an image in my support

But when I solve it for equation 2Y = X + 1 it gives me wrong result

I have to find the reflection of the point (3,-3) about 2Y = X + 1, whose answer is (-1,5) but my answer is (7,2)

HOW I DID IT.

First of All I find the corresponding point on the line 2Y = X + 1, which will be (3,2) and (-7,-3), and the corresponding reflected point will have the same value of x coordinate as (-7,-3) and same value of Y coordinate as (3,2) so the answer will be (-7,2) which is incorrect.

attached an image in my support

Please tell me where am I doing wrong?

Any other requirements or doubt in question? Please ask me in comments.