What will be the rate of interest if the simple interest earned on a sum in the third year is ₹ 1,750 and for 2 years...

If the difference between the compound interest and the simple interest earned on a sum of money at the rate of 8% p.a. for two years is Rs. 20. What is the Principal ? .

What is the rate of simple interest ? (i) The total interest earned was Rs. 4000. (ii) The sum was invested for 4 years.