Completed HW - Week 02 Day 01 - Calculator App

This homework is found in w02/d01/frederick/HW/calculator/
This calculator is fully functioning as per requirements.
I initially made it so that the result of the calculation printed on a new page called /calculator. It took perhaps an hour for me to figure out how to get this result printed below the Calculate! button. The problem just to change this line: <form action="/calculator" method="POST"> to this line <form action="/" method="POST">
This way, I assume (correct me if I'm wrong) the input values will be "posted" back to main.rb and processed. I then found no need to have the file named calculator.erb.

Please feel free to tell me if there's anything I can improve in my code :)