The name `admob' does not exist in the current context

See more:

Android

using UnityEngine;
using System.Collections;

public class Menu : MonoBehaviour {

private const string AD_UNIT_ID = "YOUR_AD_UNIT_ID";
private const string INTERSTITIAL_ID = "YOUR_AD_UNIT_ID";

private static Vector2 BUTTON_SIZE = new Vector2(100, 50);

private Rect buttonPositionShowAds;
private Rect buttonPositionHideAds;
private Rect buttonPositionShowInterstitial;


void Start() {


buttonPositionShowAds = new Rect(
(Screen.width - BUTTON_SIZE.x) / 2,
(Screen.height - BUTTON_SIZE.y) / 2,
BUTTON_SIZE.x, BUTTON_SIZE.y);

buttonPositionHideAds = new Rect(
buttonPositionShowAds.x, buttonPositionShowAds.y + BUTTON_SIZE.y * 3 / 2,
buttonPositionShowAds.width, buttonPositionShowAds.height);

buttonPositionShowInterstitial = new Rect(
buttonPositionHideAds.x, buttonPositionHideAds.y + BUTTON_SIZE.y * 3 / 2,
buttonPositionHideAds.width, buttonPositionHideAds.height);
}

void OnEnable() {

}

void OnDisable() {

}

void HandleAdLoaded() {
#if !UNITY_EDITOR
admob.ShowBanner();
#endif
}

void HandleInterstitialLoaded() {
#if !UNITY_EDITOR
admob.ShowInterstitial();
#endif
}

void OnGUI() {
if (GUI.Button(buttonPositionShowAds, "Show Ads")) {
#if !UNITY_EDITOR
admob.ShowBanner();
#endif
}

if (GUI.Button(buttonPositionHideAds, "Hide Ads")) {
#if !UNITY_EDITOR
admob.HideBanner();
#endif
}

if (GUI.Button(buttonPositionShowInterstitial, "Show Interstitial")) {
#if !UNITY_EDITOR
admob.RequestInterstitial();
#endif
}
}
}

What I have tried:

i tried to write admob global.