If x : 7.5 = 7 : 17.5, then the value of x is -

Answer: Option C

$$\begin{array}{rl}& =x:7.5=7:17.5\\ & \Rightarrow 17.5x=7.5\times 7\\ & \Rightarrow x=\frac{7.5\times 7}{17.5}\\ & =3\end{array}$$