Here,

⇒ 14% of 250× ?% of 150=840

It can also be simplified as,

$\begin{array}{l}\Rightarrow \frac{14}{100}\times 250\times x\%of150=840\\ \\ \text{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}[ taking x at the place of ?]}\\ \\ \Rightarrow \frac{14}{100}\times 250\times \frac{x}{100}\times 150=840\\ \\ \Rightarrow \frac{3500}{100}\times \frac{x}{100}\times 150=840\\ \\ \Rightarrow x=\frac{840\times 100}{150\times 35}=\frac{24\times 100}{100}=16\end{array}$

Hence, Option C is correct.