What kind of Rear derailleur do i have and what RD should I buy as a replacement?

I think you will need a claw hanger adapter. The old derailleur has one that appears to be non-removable, and the new one has a 10mm bolt that expects to find a matching hole in the frame, which yours won't have.

You probably want something that looks like this:

There is a sunrace branded one, but it looks the same in the critical dimensions as a generic pictured above.

Your derailleur looks deceptively similar to Shimano RD-TY20-GS and Shimano RD-TY15, but after taking a closer look at the embossed letters on the side, it turns out that it was manufactured by Lingxiang. It's probably model LXA-01

In case of Shimano derailleurs, the actual model name is stamped on the back [example]. Perhaps it's also true for this one.