public void SetCamera( 
   IEnumerable<Layer> layers,
   bool useSelectedFeatures
)

//Change the extent of a map frame to the selected features multiple layers.

//Perform on the worker thread
await QueuedTask.Run(() =>
{
  //Reference MapFrame
  MapFrame mf = layout.FindElement("Map Frame") as MapFrame;

  //Reference map, layers and create layer list
  Map m = mf.Map;
  FeatureLayer fl_1 = m.FindLayers("GreatLakes").First() as FeatureLayer;
  FeatureLayer fl_2 = m.FindLayers("States_WithRegions").First() as FeatureLayer;
  var layers = new[] { fl_1, fl_2 };
  //IEnumerable<Layer> layers = m.Layers;  //This creates a list of ALL layers in map.

  //Set the map frame extent to the selected features in the list of layers
  mf.SetCamera(layers, true);
});

//Change map frame extent to single feature with 10 percent buffer

//Process on the worker thread
await QueuedTask.Run(() =>
{
  //Reference the mapframe and its associated map
  MapFrame mf = layout.FindElement("Map Frame") as MapFrame;
  Map m = mf.Map;

  //Reference a feature layer and build a query (to return a single feature)
  FeatureLayer fl = m.FindLayers("GreatLakes").First() as FeatureLayer;
  QueryFilter qf = new QueryFilter();
  string whereClause = "NAME = 'Lake Erie'";
  qf.WhereClause = whereClause;

  //Zoom to the feature
  using (ArcGIS.Core.Data.RowCursor rowCursor = fl.Search(qf))
  {
    while (rowCursor.MoveNext())
    {
      //Get the shape from the row and set extent
      using (var feature = rowCursor.Current as ArcGIS.Core.Data.Feature)
      {
        Polygon polygon = feature.GetShape() as Polygon;
        Envelope env = polygon.Extent as Envelope;
        mf.SetCamera(env);

        //Zoom out 15 percent
        Camera cam = mf.Camera;
        cam.Scale = cam.Scale * 1.15;
        mf.SetCamera(cam);
      }
    }
  }
});