How to hide fields based on dropdown value

Hi, I have different kind of field I would like to hide based on a dropdown selection. There is one image : "Image1"; two buttons : "Button1" and "Button2"; ont text field : "Text8"; two checkboxes on the same name : "CB1". There is three option in the dropdown : 1, 2, 3. I would like to know what is the code to make all the field dissapear if 3 is selected. 

Thank you.