Let the rate of interest =R.
In the first 3yrs,
principal =P=Rs7000, Time T=3yrs.
Then the interest =I1=PRT100=7000×R×3100=210R.
In the next (5-3)yrs=2yrs,
Pricipal =P=RS(7000−3000)=RS4000, Time =T=2yrs.
Then, the interest=I2=PRT100=4000×R×2100=80R.
∴ the total
amount returned this time
=Rs(4000+I1+I2)=Rs5450⟹4000+210R+80R=5450⟹29R=1450⟹R=5p.c.p.a.
So the rate of interest=5% p.a.