During a march in nature scouts received a task to find out the height of tree. None of them, however, dared to climb a tree to be measured. It was therefore decided to find out its height using a length of shadow. It was 15:30 and scouts discovered that the tree casted a shadow 6 meters long. Near them stood a pillar of light, which they knew that measured 5 meters. Scouts measured his shadow and found that at 15:30 it casted a shadow 1.5 meters long. In a moment they already knew the height of the tree. How did they calculate it? How high was a tree?