Consider the following premises. t <-> w_3. ~w_3 -> s. ~t. Can we infer s from them? If possible, name the inference rules being used at each step.
 From t <-> w_3 we can infer w_3 -> t via biconditional elimination. From w_3 -> t, ~t we can infer ~w_3 via modus tollens. Finally, from ~w_3 -> s, ~w_3 we can infer s via modus ponens. Therefore, the answer is yes.