$A$ sum of money doubles itself in $8$ years. In how many years will it treble?

$Rs. 600$ becomes $Rs. 720$ in $4$ $years$ at simple interest. If the rate of interest is increased by $2 \%$,what will be the total amount (in $Rs.$)?

Asmita invests an amount of $Rs. 9535$ at the rate of $4\%$ per annum to obtain a total amount of $Rs. 11442$ on simple interest after a certain period. For how many years did she invest the amount to obtain the total sum?

Nutan borrowed some money at a rate of $4$ $p.c.p.a.$ for the first $3$ years,at the rate of $8$ $p.c.p.a.$ for the next $2$ years,and at the rate of $9$ $p.c.p.a.$ for the period beyond $5$ years. If she paid a total $SI$ of $Rs. 19550$ at the end of $7$ years,how much money (in $Rs.$) did she borrow?

The rate of simple interest (in $\%$) for which a sum of money becomes $5$ times of itself in $8$ years is:

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 $\%$).