First, present the argument that is presented in the passage. You may give a sentence or two of introduction and then give it in standard form, or you can use regular prose as you would for most papers. Do what you are comfortable with and what you think will lead to you giving the argument most clearly and concisely. Second, you are to give the best argument you can in response to the argument you just presented, i.e. give a critical argumentative response. Usually this will either be an argument that one of the premises is false (your coclusion would likely be the denial, or logically equivalent to it, of the premise in question), or an argument that shows there is a structural flaw or some other fallacy present in the argument. It should not be an argument that concludes with the denial of the conclusion of the argument you present in the first part.