Let’s suppose there are 25 questions to answer. Shauny takes 5 hours to do 25 questions, so that’s 5 questions an hour. Together they take 3⁴⁄₇=25/7 hours to answer 25 questions. So that means they answer 7 questions an hour between them. Shauny can answer 5 so Kim must answer the remaining 2 in an hour. If Kim can answer 2 questions in an hour, it takes her half an hour to answer one question, so it would take her 25 half hours to answer all 25 questions, that’s 12½ hours to do the homework by herself.