Hi Howard,
it can be done in very easy steps..
1 select entire sheet right click goto cells formating and click on protection and make sure the proteced is unchecked. and next come to sheet and select your range (i:L) and right click and goto cells formating and protection tab make sure hidden is checked and come to sheet select your range and righ click and hide .. Now goto review tab protect the worksheet with password and now it is hidden and you have to enter password to unhide it.