plan.rb

class Plan
  def price
    100
  end
end

class Promo
  def initialize(origin, code)
    @origin = origin
    @code = code
  end

  def price
    @origin.price * 0.9
  end
end

class PayPerYear
  def initialize(origin)
    @origin = origin
  end

  def price
    @origin.price * 0.9
  end
end

final_plan = PayPerYear.new(
  Promo.new(
    Plan.new,
    'SBERBANK'
  )
)