i cant find my o2 sensor

[realracersuseapc]

does anyone have a pic of under a 89 240sx and can point out where the o2 sensor is? i dont have a lift and my driveway is too slanted to jack up the car. i can get underthere enough to reach around and do everything, but im not sure where to look. and im not positive which o2 sensor to replace. i went 2 autozone and bought one and i got 1 that looked like the one in the pic i attatched. is that the 1st or 2nd one? thanks