Answer-
The total interest after 3 years is Rs.5760 .
Solution-
Total money borrowed = Rs.12000
Out of those Rs.4000 is of 18% interest rate and remaining 12000-4000=8000 is of 15% interest rate.
![\text{Total interest}=(P_1* r_1* t)/(100)+(P_2* r_2* t)/(100)](https://img.qammunity.org/2019/formulas/mathematics/high-school/hczsdngom81xdaufrrqv17ro9og0bscxmq.png)
Where,
P₁ = principal amount = Rs.4000
P₂ = principal amount = Rs.8000
r₁ = rate of interest of P₁ = 18%
r₂ = rate of interest of P₂ = 15%
t = time period = 3 years
![\text{Total interest}=(4000* 18* 3)/(100)+(8000* 15* 3)/(100)=2160+3600=5760](https://img.qammunity.org/2019/formulas/mathematics/high-school/fo8f694d2cqhbpg37rkqwg2z6kxon5kmr9.png)