Trying to move controller code to model code

gistfile1.txt

#Model Code
  def self.calculate_state_revenue(state)
    @affiliates = select_state(state) # gets all affiliates from the state
    @orders_unpaginated = self.orders

    #use inject to add up their order totals.
    @state_total = @affiliates.inject {|result, affiilate|
          result = @orders_unpaginated.calculate(:sum, "order_total", :conditions =>  ['affiliate_code = ?', affiliate.affiliate_code])
          result
          }
    @state_total
  end
#select the state, duh!
  def select_state(arg)
    #find all affiliates by the status state_active, which means they are one of the taxation states.
    your_shop.users.find_all_by_status("#{arg}_State_Active") #unless your_shop.users.blank?
  end
#controller code
  def sales_tax_states
    @shop = your_shop
  end
# View Code
<h1>Total sales for the trailing 4 quarters by state</h1>
<h2>Rhode Island</h2>
<p><%= @shop.calculate_state_revenue("RI") %></p>
<h2>New York</h2>
<p><%= @shop.calculate_state_revenue("NY") %></p>
<h2>North Carolina</h2>
<p><%= @shop.calculate_state_revenue("NC") %></p>

## Error:
undefined method `calculate_state_revenue' for #<Shop:0x105be6490>