manoj borrowed rs . 3900 from anwar at 6 % p . a . simple interest for 3 years . he then added some more money to the borrowed sum and lent it to ramu for the same time at 9 % p . a . simple interest . if manoj gains rs . 824.85 by way of interest on the borrowed sum as well as his own amount from the whole transaction , then what is the sum lent by him to ramu ?