In how many years will the simple interest on a sum of money be equal to the principal at the rate of 162/3 % per annum ?

Answer: Option C

$$\begin{array}{rl}& \text{16}\frac{2}{3}=\frac{1\to \text{ Interest}}{6\to \text{ Principal }}\\ & \text{Let principal = 6}\\ & \text{Interest = 6}\\ & \text{Time = t years}\\ & \text{By using formula }\\ & \text{6}=\frac{6\times 50\times \text{t}}{3\times 100}\\ & \Rightarrow \text{t}=6\text{years}\end{array}$$

Alternate
Note : In such type of questions to save your valuable time think like the given way.
$$\begin{array}{rl}& \text{Rate}\%\\ & \text{ = 16}\frac{2}{3}\%=\frac{1\to \text{ Interest}}{6\to \text{ Principal }}\\ & \text{Represent for 1 years}\\ & \text{According to the question,}\\ & \text{Principal = Interest}\\ & \text{6 = 1}\times \text{6}\\ & \text{Hence,}\\ & \text{Time = 1}\times \text{6}\\ & \text{ = 6 years}\end{array}$$
Note : If interest will be six times then time will also be six times.