public enum Layers
{
    Game1 = 6,
    ViewModel1 = 7,
    
    Game2 = 9,
    ViewModel2 = 10,
    
    Game3 = 12,
    ViewModel3 = 13,
    
    Game4 = 15,
    ViewModel4 = 16,
}

public static class LayerExtensions
{
    public static int ToLayerMask(this Layers layer)
    {
        return 1 << (int)layer;
    }
}