For Question 5, the correction that should be made to the underlined word "that's" is "whose." The corrected sentence should read: "We saw a bear whose paw had been damaged by a hunting trap."
For Question 6, the direct object in the sentence "The letter carrier brought my brother two large envelopes last Monday" is "envelopes." The direct object answers the question "what?" after the verb; in this case, it answers "What did the letter carrier bring?" The answer is "two large envelopes."