A single discount equivalent to three successive discount of 6%, 15% and 14% is:

Answer: Option C

$$\begin{array}{rl}& \text{Discount }\%=x+y-\frac{xy}{100}\\ & \text{2 years}\to \text{discount }\%\\ & =6+15-\frac{6\times 15}{100}\\ & =21-0.9\\ & =20.1\%\\ & \text{3 years}\to \text{discount }\%\\ & =20.1+14-\frac{20.1\times 14}{100}\\ & =34.1-2.814\\ & =31.286\%\end{array}$$