1. Get the list of people with age > 21. How many are there?

   TODO

2. Get the total and average income for the entire population.

   TODO

3. Get total and average income of people older than 21 (included).

   TODO

4. Find in which city “Mitsue Tollner” lives.

   TODO

5. Find if there is anyone who lives in the same city of others.

   TODO

6. Get the city/cities where most people live.

   TODO