If you want to be helpful still, ask what was wrong with the other 3 answers. Does he understand your answer, or disagree? Do you need to better explain your answer, or is there some missing information you didn't know about why your answer won't work? Note older workers can have issues with bad communications from young workers. I'm older, but hopefully wouldn't call someone a child (to their face anyway)... (My wife doesn't like when I don't know the answer to something, she keeps asking, maybe rewording the question thinking I'll suddenly give an answer when I didn't before...)