Consider the following premises. q_13 -> t_3. ~r_3. r_3 or q_13. Can we infer t_3 or u from them?
 From r_3 or q_13, ~r_3 we can infer q_13. From q_13 -> t_3, q_13 we can infer t_3. Finally, from t_3 we can infer t_3 or u. Therefore, the answer is yes.