It is a Rails 5.1.5 app with Ruby 2.4.2
Get the source:
$ git clone https://github.com/alexander34ro/basic-regression.git
$ cd regression
Then install the bundler gem:
$ gem install bundler
Set up the other gems:
$ bundle install
Start the server:
$ rails s
Open http://localhost:3000 in your browser to see the app running.