Set checked to radio?

Question

PHP

Hello! There is a form in the admin panel with a radiobutton, it saves the value to a file, and when I select one radio and press the Save button, checked was in the selected radio, please tell me how to do this?

Answer 1

when loading the page, read the file with the saved settings, and on the server side on the condition, add checked to the desired item. Or is it more difficult?
More or less like this.