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:

Answer: Option B

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