Rohit, Sameer and Tarun each have a field. The ratio of the areas of their fields is 3 : 8 : 3. Sameers rate of doing 'work is half that of Tarun and double that of Rohit. Each person begins the work on his field. The first person who completes the work on his field moves to that person's field in which the lesser of the work is completed. Both then complete the work on that field. After completion, they move on to the third person's, field and all complete the work on it. Tarun can complete-the work in his field in 6 hours. Find the time taken (in hours) to complete the work on all the fields.