You will need a stereo RCA audio cable to connect between the Xbox 360's L+R audio output ports and the TV's Audio input ports. A 3 plug RCA cable (with yellow, white & red plugs at both ends) will also work fine. Just use the white & red plugs and leave the yellow one disconnected at both ends.
You TV has 3 sets of L+R audio inputs. Try the them in sequence starting with the ports nearest the VGA input until you get sound.