This sequence can be modeled by

, and that if n is even, the number becomes negative. So the seventh number would be 3^6, and that is 729, since 7 is odd.
The law of demand states that other factors being constant (cetris peribus), price and quantity demand of any good and service are inversely related to each other. When the price of a product increases, the demand for the same product will fall.
that really isn't a question.
I belive the answer to the first one is no I would have to assume a habitual zone is one area on a planet. for example, an air conditioned building vs. the Savvanah dessert. However I am not sure maybe other answers will help more on this one. Sorry.... Earth-like planet would of course need water, plant life, animals, oxygen, fossil fuels etc. A challenge we would face on a travel to another liveable planet: do we have engough transportation? engough fuel to make it? How long can we live on this planet? Who or what else is present here? etc. Yes I do think they should discover a planet with earth like qualities befor investing in tools to get us to them. So money is not wasted. (make sure to put this into your own words )