If one-third of one-fourth of a number is 15, then three-tenth of that number is:

Answer: Option D

$$\begin{array}{rl}& \text{Let}\text{the}\text{number}\text{be}x\\ & \text{Then},\frac{1}{3}\text{of}\frac{1}{4}\text{of}x=15\\ & \Rightarrow x=15\times 12=180\\ & \text{So,}\text{required}\text{number}\\ & =\frac{3}{10}\times 180\\ & =54\end{array}$$