Consider the following premises. w -> r_8. t or ~r_8. t -> w. Can we infer ~(r_8 -> t) from them?
 From t -> w, w -> r_8 we can infer t -> r_8. Finally, from t or ~r_8 we can infer r_8 -> t, which contradicts ~(r_8 -> t). Therefore, the answer is no.