Breakdown

Hi, the citizens argument is that the mayor must have some other motive than attracting business because the business park would bring in twice as much business as the highway. Since the first sentence is the conclusion we don't have to take it as a fact. For necessary assumptions we are looking to find something that must be true if the argument makes sense (and thus if negated would destroy the argument). If the mayor disagreed that the business park would bring in more revenue, or were unaware that it was even an option, then the citizen groups argument would make no sense, since it's possible the mayor was choosing what they legitimately think is the best way to bring in new business.