Consider the following premises. q_1 <-> t_2. u_4 -> w. ~w. q_1 -> u_4. Can we infer ~t_2 from them?
 From u_4 -> w, ~w we can infer ~u_4. From q_1 -> u_4, ~u_4 we can infer ~q_1. Finally, from q_1 <-> t_2, ~q_1 we can infer ~t_2. Therefore, the answer is yes.