Deraileur Question

[obi]

Hi i am doing up a bike thats about 10yr old i was gonna order a derailleur of ebay but there is all sorts, how do i know which to order? i have 3 bikes and they are all different . the bike is a carrera kraken. ive attached a pic . cheers

[nfmisso]

http://www.amazon.com/Shimano-Tourney-TX35-Derailleur-Speed/dp/B003ZMH69S/

will work fine. The freewheel does NOT look good, and should be replaced, along with the chain.