Can't Hide AdMob Ads Banner

guys im in very beginning learning code in unity. I have my AdMobs script which places the banners, which I just want to place it on my shop screen. but I have problem coding it
everyone in internet said if we want to hide the banner ads, we just had to put simple code like
bannerView.Hide ();
but when I try it, my monodevelop said that “bannerView” doesnt exist

here is my code

![void Start () {
		// Create a 320x50 banner at the top of the screen.
		BannerView bannerView = new BannerView("ca-app-pub-xxxxx/xxxxxx", AdSize.Banner, AdPosition.Top);
		// Create an empty ad request.
		AdRequest request = new AdRequest.Builder()
			.AddTestDevice(AdRequest.TestDeviceSimulator)       // Simulator
			.Build();
		// Load the banner with the request.
		bannerView.LoadAd(request);
	}

void Update()
	{
		
		if (shopscreen.activeInHierarchy == true)
		{
			bannerView.Hide ();
			Debug.Log("SHOW AD banner");
		}
		else if(shopscreen.activeInHierarchy == false)
		{
			bannerView.Show();
		
	}][1]

help please …

You have to declare BannerView variable outside of the method, so that you can use it anywhere and not just the method you declared it into. Like so:

private BannerView bannerView;

void Start() {
bannerView = new BannerView("ca-app-pub-xxxxx/xxxxxx", AdSize.Banner, AdPosition.Top);
//blabla
}

void Update() {
bannerView.Hide();
//blabla
}