PII (Personally identifiable information) is any data that will be useful in identifying a particular individual e.g full name, date of birth, etc. A donors detail in the database will surely be the data to be used to identify him personally.
Each of the 20 people has 19 other people to communicate to. If you add that all up you get 20*19 paths, but then each path is counted twice (back and forth), so we divide this by 2. 20*19/2 = 190.
