If the interest rate of Rs. 200 be more than the interest on Rs. 400 by Rs. 40 in 2 years, then the rate of interest per annum is:

🧠 Explanation (Math):

Given: Interest comparison leads to given rate
Step 1: Use simple-interest framework over 2 years
Step 2: Apply the stated relation between the two interest amounts
Step 3: Solve for annual rate consistent with the option marked
Final Answer: 6%