Explain in detials:

1. Why do we need to assume other things equal (constant) when justifying the law of demand? Explain in details with an example.

2. What should OPEC (The Organization of the Petroleum Exporting Countries) do if they want to increase their revenue?

3. In most countries, government policy to eliminate narcotic problem is to catch narcotic producers/sellers, i.e. reducing supply. Why might the policy turn out to make narcotic producers better off (financially)? What should be a better policy to eliminate the narcotic problem?