You'll notice above I used "@@wheels" -- this indicates a class variable... Or a variable for the entire Automobile class.

to set it:

```ruby
class Automobile < Vehicle
  @@wheel = 4
end
```

And to be able to return its value:

```ruby
class Automobile < Vehicle
  @@wheel = 4

  def self.wheel
    @@wheel
  end
end

Automobile.wheel
 => 4
```