To determine which of the three objects casts the longest shadow, we need to convert their heights to the same unit. Let's convert everything to feet:
-
Building:
Height = 20 feet -
Tree:
Height = 252 inches
To convert inches to feet:
\( \text{Height} = \frac{252}{12} = 21 \text{ feet} \) -
Flagpole:
Height = 6 yards
To convert yards to feet:
\( \text{Height} = 6 \times 3 = 18 \text{ feet} \)
Now we have the heights in feet:
- Building: 20 feet
- Tree: 21 feet
- Flagpole: 18 feet
Given that the tree is the tallest at 21 feet, it would cast the longest shadow under the same lighting conditions (assuming similar angles of sunlight).
So, the answer is the tree.