A sum of  Rs.14000 amount to Rs.$22,400$ in $12\text{years}$ at the rate of simple interest. The rate of interest is

Given  P$=$ Rs.14000 , A$=$ Rs.$22,400$  , T$=$ 12 years

$\text{A}=\text{P}+\text{I}$

$\text{A}-\text{P}=\text{I}$

Rs.$22,400$ $-$  Rs.14000 $=$ Rs. 8400

Rs. $8400=\text{I}$  

$\text{simple}\text{}\text{interest}\left(\text{I}\right)=\frac{\text{PTR}}{100}$

$8400=\frac{14000\times 12\times \text{R}}{100}$

$8400=140\times 12\times \text{R}$

$\frac{8400}{140\times 12}=\text{R}$

$\frac{70}{14}=\text{R}$

$\text{R}=5\%$