A certain sum of money amounts to Rs.1300 in 2 years and to Rs. 1525 in 3.5 years. Find the sum and the rate of interest ?

1525 – 1300 = 225 for 1.5 yrs (3.5 – 2)
So for one yr 225 / 1.5 = 150
then for 2 yrs interest is 150 + 150 = 300
Then principal 1300 – 300 = 1000.
Now 150 / 1000 * 100 = 15%