The sentence in which the underlined verb is used correctly in the subjunctive mood is the one that reads "if I were you, I would try out for the lead in the school play".
In the English language, the subjunctive mood is used to talk about conditional or imaginary situations. In this case, it has been used to explore a condition which is contrary to fact, that is, the person speaking is not the addressee. That is why the sentence reads "if i were you". It is a piece of advise.