Oracle - Help with Queries - Working on Mondial Database

Hello there...

I hope there is someone who is working with Mondial database for Oracle. I have few problems with finding results tru queries for the following tasks:

1) For all countries, give the sum of the population of all its neighbours (take all countries into account)

2) Compute all political organizations that have at least one member country on every continent
(don’t consider differnt types of memberships). Why is this operation called relational division?.

3) For every organization, give the length of its borders to countries that do not belong to this
organization.

4) State an SQL query that computes all landlocked countries that have borders just with other
landlocked countries.

Bellow is the Database Relational Diagram!

Hope someone is there able to help me..

Thanks in Advance,
HKD

->> webfreedownload.net/LABS/mondial_RELATIONAL.bmp