There is a pile of six boxes. The weight of the topmost box
i.e., 6th box is one fifth of the second box, the weight of the first box is 25% less than the weight of the fourth box, whose weight is thrice that of fifth box’s weight. Also, weight of second box is 2.5 times the fifth box. The third box whose weight is 720 gm is 60% heavier than the fifth box. What is the average wt. of the three lightest boxes?