Do something When trackable image appears

I am new here so i want to ask my first question. I am using unity3d and vuforia for augmented reality.

I already seted up AR camera on me scene, target image and object and works perfect.

I am trying to play a sound when my 3d model appears on stage but without any luck.

So far i tried to follow this tutorial: https://www.youtube.com/watch?v=4u177CpPbp8 but in the line public class PlaySoundOnImageTarget : MonoBehaviour, ITrackableEventHandler comes with an error on ITrackableEventHandler.

It's red colored and when i am moving my mouse on this it says: error CS0103: the name ITrackableEventHandler does not exists in the current context.

I tried to write the full code but a lot of lines comes with almost the same errors.

Also i tried this one: https://developer.vuforia.com/forum/faq/unity-how-can-i-play-audio-when-targets-get-detected but i got the same errors in code.

Any help please?

I am using unity3d 5.4.2f2