If a% of x is equal to b% of y, then of c% of y is what % of x ?

Answer: Option B

$$\begin{array}{rl}& \frac{ax}{100}=\frac{by}{100}\\ & or,ax=by\\ & \Rightarrow y=\frac{ax}{b}\\ & c\%\text{of}y=\frac{cy}{100}\\ & or,\frac{cy}{100}=\frac{cax}{100b}\\ & \text{Thus},\\ & c\%\text{of}y=\frac{ca}{b}\%\text{of}x\end{array}$$