If the amount received at the end of the 2nd and 3rd year at Compound Interest on a certain Principal is $\text{Rs }28090$ and $\text{Rs }29775.4$ respectively, what is the rate of interest?

In compound interest, the amount at the end of the 2nd year acts as the principal for the 3rd year.Amount at the end of 2nd year ($A_2$) = $\text{Rs }28090$ Amount at the end of 3rd year ($A_3$) = $\text{Rs }29775.4$ The interest earned in the 3rd year is:
$$\text{Interest}=A_3-A_2=29775.4-28090=\text{Rs }1685.4$$
The rate of interest ($R$) can be computed as:
$$R=\left(\frac{\text{Interest earned in 3rd year}}{A_2}\right)\times 100\%$$
$$R=\left(\frac{1685.4}{28090}\right)\times 100\%$$
$$R=\frac{168540}{28090}=6\%$$