Consider the following premises. ~u. u or ~u_4. t and r_1. Can we infer ~u_4 and t from them?
 From u or ~u_4 we can infer u_4 -> u. From u_4 -> u, ~u we can infer ~u_4. From t and r_1 we can infer t. Finally, from ~u_4, t we can infer ~u_4 and t. Therefore, the answer is yes.