Final answer:
Ralph insists on washing and cleaning up before visiting Jack's tribe to maintain good hygiene, fit in with the cleanliness standards of the people in Baltimore, and to receive a reward of a pair of trousers.
Step-by-step explanation:
Ralph insists on washing and cleaning up before visiting Jack's tribe for several reasons. Firstly, he wants to maintain good hygiene and cleanliness, as the people in Baltimore, where he is going, value cleanliness and would laugh at him if he looked dirty. Secondly, Ralph's motivation to clean up is driven by the promise of receiving a pair of trousers, which he sees as a great reward. This shows that Ralph is willing to put in the effort in order to be presentable and fit in with the people he is visiting.