Answer: 180 feet
Step-by-step explanation:
Given: A 50-foot flagpole is at the entrance of a building that is 300 feet tall.
Them two right triangles must be formed by flagpole and building with the ground and are similar because the angle of the sun is the same at the same time of day.
So by the properties of similar triangles,
1) All the three angles of each triangle must be equal to a corresponding angle of the other triangle.
2) Sides are proportional to the corresponding sides in the other triangle,
Therefore, the length of building's shadow is 180 feet.