$6.4 - 1.6 \div 0.2 = ?$

If $N = \frac{\sqrt{7} - \sqrt{3}}{\sqrt{7} + \sqrt{3}}$,then what is the value of $N + \frac{1}{N}$?

The rational number for the recurring decimal $0.125125 \ldots$ is

If $x=(\sqrt{2}-1)^{-1/2},$ then the value of $\left(x^{2}-\frac{1}{x^{2}}\right)$ is

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

Simplify:
$\frac{3}{10} \div \frac{3}{7} \text{ of } \left(2 \frac{3}{10} + 2 \frac{3}{5}\right) + \frac{1}{5} \div 1 \frac{2}{5} - \frac{2}{7}$