Added total cost method

lib/reservation.rb

@@ -0,0 +1,18 @@
+module Hotel
+  class Reservation
+    attr_reader :dates
+
+    ROOMCOST = 200
+
+    def initialize(checkin_date, checkout_date)
+      @dates = DateRange.new(checkin_date, checkout_date)
+      @num_nights = checkout_date - checkin_date
+    end
+
+    def price_night
+      total_cost = (@num_nights-1) * ROOMCOST
+      return total_cost
+    end
+  end
+
+end