1st you will need to know what version of Corel they have
2nd you'll need to know what versions of .ai 'that' version of corel can open (yes corel will open an .ai file)
3rd save as .ai and back save to a earlier version that's compatible with Corel
you will get the 'options' menu after you select save--there is a drop down menu to choose an earlier version--see attached
