i) Some genius will answer that..
ii) An a/c flying at 3000ft on 990 will not be separated from someone flying at FL40 on 1013 as they will be only 300-odd feet apart.
Here's a tip from an instructor of mine when I was a kid - helps with all altimeter questions. If you wind the subscale up, the altimeter reading goes up. So... if the subscale is at 990 and the altimeter is reading 3000 ft.... if you turn the subscale up to 1013 the altimeter reading increases to around 3690 ft. It may sound simply but it answers question ii.
Good luck...