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

$A$ man invests ₹ $3965$ in the names of his three daughters,Neeta,Sita,and Gita,in such a way that they would receive the same amount after $2, 3,$ and $4$ years. If the rate of interest is $5 \%$ p.a.,then the amount (in ₹) invested for Neeta,Sita,and Gita is:

The simple interest on ₹ $500$ at $6 \%$ per annum from $May$ $3^{rd}$ to $July$ $15^{th}$ in the same year is (in ₹):

Adam borrowed some money at the rate of $6 \% \text{ p.a.}$ for the first two years,at the rate of $9 \% \text{ p.a.}$ for the next three years,and at the rate of $14 \% \text{ p.a.}$ for the period beyond five years. If he pays a total interest of ₹ $11,400$ at the end of nine years,how much money (in ₹) did he borrow?

$A$ lent ₹ $5,000$ to $B$ for $2$ years and ₹ $3,000$ to $C$ for $4$ years on simple interest at the same rate of interest and received ₹ $2,200$ in all from both of them as interest. The rate of interest (in $\%$) per annum is:

The rate percent per annum at which ₹ $1200$ amounts to ₹ $1440$ in $4$ years is: