In a factory there are 100 skilled, 250 semi-skilled, and 150 unskilled workers. It has been observed that on an average a unit length of a particular fabric is woven by skilled workers in 3 hours, by a semi-skilled worker in 4 hours, and by an unskilled worker in 5 hours. Unskilled workers are expected to become semi-skilled workers and semi-skilled workers are expected to become skilled. How much less time will be required after 2 years of training for weaving the unit length of fabric by an average worker?​