For 8 have you tried just writing out a few of the sets to see what sets you are dealing with? For example, (b) says the sets are .
For n= 1, that is . For n= 2, . For n= 3, . Each of those sets is contained in the previous one. So the union is just the biggest set, the first one. The intersection will be numbers that are in all them. Of course, goes to 0 as n goes to infinity. The right boundary is always 1.
For 9, is the set of all rational numbers between 0 and x. What happens as x gets larger and larger?