Three women Neha, Priya and Sneha are working on a task. Working alone, Neha, Priya and Sneha take 12, 15 and 20 hours to complete the task respectively. Neha and Priya worked for the first hour and then Neha and Sneha worked for the next hour. This pattern is continued until the work is finally finished. Determine the time taken to finish the task in this manner. (in hours)