20 feet
Any height.
When the Sun is low, in the morning or evening close to the horizon, even a short object will cast a long shadow. When the Sun is directly overhead (at noon between the Tropic of Capricorn and the Tropic of Cancer) objects cast no shadow.
If you tell us your location and the time you are measuring then there would be a possibility of calculating an answer.
The ratios are in the same proportion, so all you need to really figure out is what is in the same ratio to 20 as 6 is to 4.
It is approx 36.6 ft.
21
25
Ratio of object to its shadow is the same. So if T is the height of the tree, then T/21 = 4/6 So T = 21*4/6 = 84/6 = 14 feet
28 feet
To cast a 19 foot shadow the building would have to be 26.91 feet tall. Each foot of building/tree casts 8.47 inches of shadow.
35 feet tall.
6 feet
25 feet tall
60 inches, or 5 feet.
It works out as: 42.353 feet tall rounded to 3 decimal places
The height of the flagpolle is 26.25 feet
63 feet
A 1 foot shadow I think.
36.0 feet
It is 90 feet in height