For what sum (in ₹) will the simple interest at $R \%$ per annum for $2$ years be $R$?

$A$ person lent ₹ $10000$ to $B$ for $3$ $years$ and ₹ $6000$ to $C$ for $4$ $years$ on simple interest at the same rate of interest and received ₹ $5400$ in all from both of them as interest. What is the rate of interest (in $\%$)?

Manish borrowed a sum of $Rs. 1150$ from Anil at the simple rate of $6$ $p.c.p.a.$ for $3$ years. He then added some more money to the borrowed sum and lent it to Sunil for the same time at $9$ $p.c.p.a.$ at simple interest. If Manish gains $Rs. 274.95$ by way of interest on borrowed sum as well as his own amount from the whole transaction,then what is the sum (in $Rs.$) lent by him to Sunil?

Nitin borrowed some money at the rate of $6 \% \text{ p.a.}$ for the first three years,$9 \% \text{ p.a.}$ for the next five years,and $13 \% \text{ p.a.}$ for the period beyond eight years. If the total interest paid by him at the end of eleven years is ₹ $8,160$,the money borrowed by him was:

If a sum of money at simple interest doubles itself in $6$ years,it will become four times in how many years?

Hemant makes a fixed deposit of $Rs. 20000$ in Bank of India for a period of $3 \,yr$. If the rate of interest is $13 \%$ $SI$ per annum charged half-yearly,what amount (in $Rs.$) will he get after $42 \,months$?