If the difference between $\frac{4}{5}$ part and $\frac{3}{4}$ part of a number is $4,$ what is the number?

Seema bought $20$ pens,$8$ packets of wax colours,$6$ calculators,and $7$ pencil boxes. The price of a pen is $Rs. 7$,a packet of wax colour is $Rs. 22$,a calculator is $Rs. 175$,and a pencil box is $Rs. 14$ more than the combined price of one pen and one packet of wax colours. How much amount did Seema pay to the shopkeeper? (in $Rs.$)

$A$ printer numbers the pages of a book starting with $1$ and uses $3189$ digits in all. How many pages does the book have?

Evaluate $\frac{(2.39)^{2}-(1.61)^{2}}{2.39-1.61}$

$12 \frac{5}{7} + 23 \frac{3}{5} - 14 \frac{1}{3} = 28 \frac{4}{7} - ?$

$\frac{\sqrt{1296}}{?} = \frac{?}{2.25}$