Done

application.rb

@@ -2,7 +2,7 @@ class Application
 
   def call(env)
     resp = Rack::Response.new
-    resp.write "Hello, World"
+    resp.write "Hello, my name is"
     resp.finish
   end
 

first.ru

@@ -0,0 +1,9 @@
+require 'rack'
+
+
+
+my_server = Proc.new do 
+  [200, {'Content-Type' => 'text/html'},['<em>Hello my web app example</em>']]
+end 
+
+run my_server

my_server.rb

@@ -0,0 +1,9 @@
+class MyServer
+  def call(env)
+    return [ 200, {'Content-Type' => 'text/html'}, pretty_response ]
+  end
+
+  def pretty_response
+    (Time.now.to_i % 2).zero? ?  ["<em>Hello</em>"] : ["<strong>Hello third example class/rb and ru files</strong>"]
+  end
+end

second.ru

@@ -0,0 +1,15 @@
+require 'rack' 
+
+class  MyServer 
+
+  def call(env)
+
+    return [ 200, {'Content-Type' => 'text/html'}, pretty_response ]
+  end
+
+  def pretty_response
+    (Time.now.to_i % 2).zero? ?  ["<em>Hello</em>"] : ["<strong>Hello</strong>"]
+  end
+end
+
+run MyServer.new

third.ru

@@ -0,0 +1,2 @@
+require_relative './application'
+run Application.new