Correct Option: B

As per the given in question ,
A sum of ₹ P becomes ₹ 2P in 4 years.
Similarly, ₹ 2P will become 2 × 2P = ₹ 4P in next 4 years and ₹ 4P will become 2 × 4P = ₹ 8P in yet another 4 years. So, the total time = 4 + 4 + 4 = 12 years
Second Method to solve this question :
Here, m = 2, t = 4
Time taken to become 2³ = n × t years
Required Time = 3 × 4 = 12 years
Note : - If a sum of money becomes n times in t years, it will become t¹ = n^y times at the same rate of interest in t¹ years given by,
[t¹ = yt]