$\frac{4.2 \times 4.2 - 1.9 \times 1.9}{2.3 \times 6.1} = ?$

What is the value of $\frac{2.75 \times 2.75 \times 2.75 - 2.25 \times 2.25 \times 2.25}{2.75 \times 2.75 + 2.75 \times 2.25 + 2.25 \times 2.25}$?

$47 \frac{1}{17} \div 1 \frac{49}{51} + 23 \frac{5}{7} + ? = 67 \frac{4}{9}$

If $P = \frac{(\sqrt{7} - \sqrt{6})}{(\sqrt{7} + \sqrt{6})},$ then what is the value of $\left(P + \frac{1}{P}\right)?$

What will come in place of the question mark (?) in the following expression?
$(4444 \div 40) + (645 \div 25) + (3991 \div 26) = (?)$

If we multiply a fraction by itself and divide the product by its reciprocal,the fraction thus obtained is $18 \frac{26}{27}$. The fraction is