First: Check the owner's manual. If you're lucky, sometimes the dealer or former owner will have written down the code number somewhere in the manual (inside the front cover or on the page that...
Mine was written on top of radio.Pull it out and have a look.
Maybe you do not need to remove the radio. Go to the Honda website and sign up for the Owner's Link. You will be able to get the code there.
In the book that comes with the car, or from a Mitsubishi dealership...
If you open your middle console, there is a white sticker with a 5 digit code. That is your radio code.