Answer: 48 ft
Step-by-step explanation:
Given
Height of street light h=12 ft
length of shadow x=18 ft
Shadow length of building x'=72 ft
suppose the height of the building is y
from the figure, we can write

1. 180
2. 1&4
3. 1
the answer to the question
X is multiple of 9 as well as 12.
Thus, smallest value will be 36 ( 9 *4 = 36, 12 * 3 = 36)
3 and 12 are not the multiples of 9.
72 is a larger multiple than 36; thus, the correct answer is 36.