Dear Surajit,
The questions 2,5,6 that you have mentioned are related to intervals. Please go through the lecture again and observe how an interval is defined, then you can solve the respective questions. Next, for question 7, the total number of subsets of a set is basically the number of elements in the power set of the given set.
Hope this helps
Regards
srikanth venkatesan
IITM Online degree project
3rd floor, IC&SR building, IIT Madras.