Mr. Irani borrowed a sum of ₹ $10000$ from a finance company for $6$ years at $8 \%$ per annum. The amount (in ₹) returned by Mr. Irani to the finance company is:

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

In how many years will a sum of money treble itself at $10 \%$ per annum simple interest?

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 $42 \,months$?

$A$ certain sum is invested for a certain time. It amounts to ₹ $450$ at $7 \%$ per annum. But when invested at $5 \%$ per annum,it amounts to ₹ $350$. Find the sum (in ₹).

The population of Mumbai increases by $5 \%$ per annum. Its population was $100000$ in $2004$. What was its population after $3$ years?