vehicle.rb

# Superclass
class Vehicle
  MILES_PER_GALLON = 20

  attr_reader :fuel

  def initialize
    @fuel = 0
  end

  def add_fuel(amount)
    @fuel += amount
  end

  # How far can we go?
  def range
    @fuel * MILES_PER_GALLON
  end

  def steer
    'Turn front 2 wheels'
  end
end