2. Calculate the average elevation, grouped by country id, in the airports table ordered by the average elevation in descending order for any country that has an average elevation of at least 300.
4. Provide the query to determine how many aircrafts does "Boeing" have that starts with "74".
6. Provide the query to determine how many different wake sizes do "Boeing" and "Airbus" have?
8. Provide the query to determine how many active airlines are present in Canada. You will need 2 queries.