My teacher never taught us this, so I'm not really sure if my answer is right,
You notice that more aid is given to the countries that are near ours. This is probably due to security, by forming a good relationship, we also form a good security around our country. Resources can also be a factor. PNG is apparently very undeveloped, hence there are many resources available in the country, by forming a good relationship PNG would give a fraction of these resources to Australia.
And yea, as theind had said, we can help you but not do your homework step by step etc... for good reasons.