In how many least number of complete years a sum of money become more than four times of itself at the rate of 50% per annum on simple interest?

Answer: Option C

$$\begin{array}{rl}& \text{SI}=\frac{\text{PRT}}{100}\\ & 3x=\frac{x\times 50\times \text{T}}{1.0}\\ & \text{T}=\frac{3\times 100}{50}\\ & \text{T}=6\end{array}$$
In T = 6 yrs it will become 4 times
For making it more than 4 time check what the time least time after 6 years in option.