At what rate per cent of simple interest will a sum of money double itself in $12$ years?

$A$ 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 $\%$)?

Rakesh borrowed ₹ $5000$ from Ganesh at simple interest. If Ganesh received ₹ $500$ more than his capital after $5$ years,then the rate of interest (in $\%$) per annum is:

If the simple interest on a certain sum of money for $2$ $years$ is one-fifth of the sum,then the rate of interest (in $\%$) per annum is

Mayuri took a loan at a simple interest rate of $6 \, p.c.p.a.$ in the first year,and the rate increased by $1.5 \, p.c.p.a.$ every year. If she paid $Rs. 8190$ as interest at the end of $3 \, years$,what was her loan amount (in $Rs.$)?

Rashmi lent $Rs. 600$ to Geeta for $2 \,yr$ and $Rs. 150$ to Seeta for $4 \,yr$ at the same rate of interest and received altogether $Rs. 80$ as simple interest from both. Find the rate of interest (in $\%$).