A flagstaff 17.5 m high caste 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 be x metres
Lees lengthy shadow, Less is the height (Direct proportion)
$$\begin{array}{rl}& \therefore 40.25:28.75::17.5:x\\ & \iff 40.25\times x=28.75\times 17.5\\ & \iff x=\frac{\left(28.75\times 17.5\right)}{40.25}\\ & \iff x=12.5\end{array}$$