A flagstaff 17.5 m high casts a shadow of length 40.25 m. The height of the building, which casts a shadow of length 28.75 m under similar conditions will be:

Let the height of the building x metres.
Less lengthy shadow, Less in the height (Direct Proportion)
$$\eqalign{ & \therefore 40.25:28.75::17.5:x \cr & \Rightarrow 40.25 \times x = 28.75 \times 17.5 \cr & \Rightarrow x = \frac{{28.75 \times 17.5}}{{40.25}} \cr & \Rightarrow x = 12.5 \cr} $$