Quite surprised that your cassette is 11-42 (NB 9 speed). That implies that your RD is managing a range of 51 (42-11=31; 48-28=20). Suspect 11-32 (and I can count 8 teeth in a quadrant of the image).
I would try to get the indexing sorted ie adjusted properly before replacing the cable.
Took the cable off,pushed the derailleur by hand and it won't sellect the top and bottom gears.My thinking it's not the right one for a 9 speed cassette.
You have two limit screws: an H and an L. Unscrew them a couple of turns. Then index the gears - plenty of
videos to help you (search for yourself) - needs a bit of patience.
the chain ring is very worn so need a new one
Recommend, before precipitate purchase, you take photo (from the side) of the chainring (teeth) and post it for us to assess. Which of the three chainrings btw?
As
@bikingdad90 says: the outer cable is way too short - when you replace the cable, replace the outer at the same time and give it more of a loop - an extra 5cm, perhaps.
There'sit of play in the cassette,just a bit.is that normal.
Can you be more explicit, please? play side-to-side? is the lockring tight? Maybe you need a spacer in there (depends on depth of freehub).