At what rate per cent per annum will ₹ 630 produce an interest of ₹ 126 in 4 years?

Given:

P = ₹ 630

T = 4 years

S.I. = ₹ 126

Let rate of interest be $r$.

$\because \text{S.I.} = ₹ \Big(\dfrac{P \times R \times T}{100}\Big)\\[1em] \Rightarrow \text{126} = ₹ \Big(\dfrac{630 \times r \times 4}{100}\Big)\\[1em] \Rightarrow \text{126} = ₹ \dfrac{2,520r}{100}\\[1em] \Rightarrow \text{126} = ₹ \dfrac{252r}{10}\\[1em] \Rightarrow r = \dfrac{126 \times 10}{252}\\[1em] \Rightarrow r = 5$

Hence, the rate of interest = 5%.