The simple interest on a certain sum of money for \(2\frac{1}{2}\) years at 12% per annum is Rs. 40 less than the simple interest on the same sum for \(3\frac{1}{2}\) years at 10% per annum. Find the sum.

• A. Rs. 450
• B. Rs. 600
• C. Rs. 700
• D. Rs. 800