hello!
Parallel lines have the same slope.
So if we're asked to identify a pair of parallel lines, we can just take a look at the slope (the number before x)
The first one is y=3x-5. Okay.
The second one is y=-3x+7. So the second line isn't parallel to the first line.
The third line is y-3x=12, or y=3x+12.
So the 3rd line is parallel to the 1st line :)
note:-
Hope everything is clear; if you need any clarification/explanation, kindly let me know, and I'll comment and/or edit my answer :)