In a partnership firm two partners, Vijay and Praveen are working on an ssignment. It will take 12 weeks for Vijay to complete the entire assignment alone, while Praveen will take 8 weeks to complete it alone. Due to work pressure, they decided to work on that assignment on the alternate week basis. In the first week Praveen will work and in the second week Vijay will work and so on. In how many weeks the work will be completed if they work on alternate week basis?