The simple interest earned on Rs. 2,800 at a rate of 10% per annum for 3 years is Rs. x, and Rs. 1,736 is the simple interest earned on Rs. 6,200 at a rate of 14% per annum for y years. What is the value of xy?

A sum becomes 25 times of itself when invested for 48 years at r% simple interest per annum. Find the compound interest earned if Rs. 51,200 is invested at r% per annum when interest is compounded half-yearly, for 1.5 years.

Simple interest on a certain sum at 4% per annum for 2 years is ₹80. What is the compound interest on the same sum for the same period at the same rate?