They key here is that the person and their shadow make a similar triangle to the tree and its shadow. That means the ratio between the height of the person and their shadow, will be the same ratio as the height of the tree and it's shadow. Therefore, we can write the following equation,
Let x be the height of the tree.
5.5 / 128 = x / 190
Now solve for x.
0.04297 = x / 190
190(0.04297) = x
8.164 = x
So the height of the tree is 8.164 feet
