Answer
Find out the what is the height of the building.
To prove
Let us assume that the height of the tree be x .
Let us assume that the shadow of the tree be y .
x = ky
Where k is the constant of proportionality.
As given
A 21 meter tall tree near a building casts a shadow that is 24 meters long.
21 = k × 24
k = 0.875
Let us assume that the height of the building be u .
As given
The building casts a shadow that is 56 meters long.
put values in the x = ky
u = 0.875 × 56
u = 49 cm
Therefore the height of the building is 49 cm .