A worker borrowed some money on simple interest at the rate of 6% p. a. for the first 3 years, at the rate of 9% p. a. for the next 3 years, and at the rate of 14% p. a. for the period beyond 6 years. If he paid a total interest of Rs. 6,490 at the end of 7 years, how much money did he borrow?

Let the principal sum borrowed be P.
The total time period is 7 years, broken down as follows:

First 3 years at 6% per annum

Next 3 years at 9% per annum

Remaining period =7−6=1 year at 14% per annum

Total simple interest paid:

SI=
100
P×6×3
​
+
100
P×9×3
​
+
100
P×14×1
​

6490=
100
18P+27P+14P
​

6490=
100
59P
​

59P=6490×100
P=
59
649000
​
=11,000
Therefore, the money borrowed was Rs. 11,000.