A man was 32 years of age when he had his first son. His wife was 35 years of age when his son attained the age of 7 years. The difference between the age of the father and the mother is _____
A can do 1/3rd of a job in 3 days and B can do half of the job in 9 days. If they work on it together, then in how many days can they finish half of the job?