In American English we'd use the word "amount" instead of "sum", and also we'd use the dollar symbol ($) instead of RS (rupees). Instead of "argues," use the word "agrees."
<span>A man borrowed a sum of money and agrees to pay $4820 at the end of the 2nd year and $4200 at the end of the 3rd year to clear the debt. Interest is compounded annually at 5% per annum .find the original amount borrowed.</span>