Question: How many elements are in each set?
For the first set, I think it's 8995 because the set is the union of {1,2,3,4,5},{1,2,3,4,5,6},...{1,2,3,...9000}. So 9000 - 5 = 8995.
For the second set, I'm not too sure about counting the elements in the set. Since $$1<x≤i$$, I can't think of...