Final answer:
The direct object pronoun 'le' can be used to replace the direct object noun 'le sac à couchage' in the sentence 'Où est-ce que tu mets le sac à couchage?'
Step-by-step explanation:
In order to replace the direct object noun 'le sac à couchage' (the sleeping bag) with a direct object pronoun, you can use 'le' which represents 'it' or 'him' in this context. Therefore, the sentence 'Où est-ce que tu mets le sac à couchage?' can be rewritten as 'Où est-ce que tu le mets?'.
Learn more about Direct object pronouns in French