Consider the following premises. r or ~t. u_2 -> t. u_3 -> u_2. Can we infer u_3 -> r from them?
 From r or ~t we can infer t -> r. From u_3 -> u_2, u_2 -> t we can infer u_3 -> t. Finally, from u_3 -> t, t -> r we can infer u_3 -> r. Therefore, the answer is yes.