Consider the following premises. r_3. p_6 or p_4. p_6 -> u. p_4 -> u. Can we infer r_3 and u from them?
 From p_6 -> u, p_4 -> u, p_6 or p_4 we can infer u. Finally, from r_3, u we can infer r_3 and u. Therefore, the answer is yes.