In what time will ₹ $8100$ produce the same income at $3 \%$ as ₹ $225$ in $4$ years at $3 \%$?

$A$ money lender lends ₹ $400$ for $3$ $years$ to a person and ₹ $500$ for $4$ $years$ to another person at the same rate of simple interest. If altogether he receives ₹ $160$ as interest,what is the rate of interest per annum (in $\%$)?

Nutan invests $Rs. 22400$ at a Simple Interest $(S.I.)$ rate of $12$ $p.c.p.a.$ How much amount will she receive after $7$ years (in $Rs.$)?

If the annual rate of simple interest increases from $10 \%$ to $12 \frac{1}{2} \%$,a man's yearly income increases by ₹ $1250$. His principal (in ₹) is

$A$ person invested $\frac{2}{3}$ of his capital at $3 \%$,$\frac{1}{6}$ at $6 \%$,and the remainder at $12 \%$. If his annual income is $₹ 25$,then the total capital (in $₹$) is:

$A$ certain sum doubles in $7$ years at simple interest. The same sum under the same interest rate will become $4$ times in how many years?