Why I am receiving an error message about cannot load such file

When i run the program I am receiving this error message: require_relative 'models/pets.rb'

appication_controller.rb

require 'bundler'
Bundler.require
require_relative 'models/pets.rb'

 class ApplicationController < Sinatra::Base

  get '/' do
    #home
    erb :index
  end
  get '/questions' do
    erb :questions
  end
post '/results' do 
  @dog=get_results(params)

  erb :results
end
end