Least Upper Bounds

Problems:

Question Number	Difficulty	Completed
1	()	No
2	()	No
3	()	No
4	(*)	No
5	()	No
6	(*)	Yes
7	()	No
8	(*)	No
9	(*)	No
10	()	No
11	()	No
12	()	No
13	()	No
14	()	No
15	(*)	No
16	(*)	No
17	()	No
18	(*)	No
19	(*)	No
20	()	No