If $(\frac{5}{9} \text{ of } x) - (\frac{2}{5} \text{ of } \frac{9}{4}) = -\frac{4}{5}$,then find $x$.

Determine the value of $x$. If $x = \frac{(943 + 864)^{2} - (943 - 864)^{2}}{(1886 \times 1728)}$

What will come in the place of the question mark $(?)$ in the following expression?
$59.88 \div 12.21 \times 6.35 = ?$

What will come in place of the question mark (?) in the following expression?
$5 \frac{17}{37} \times 4 \frac{51}{52} \times 11 \frac{1}{7} + 2 \frac{3}{4} = ?$

$7^{5} \div 7^{3} \div 7^{2} \times 7^{4} \times \frac{1}{7^{3}} = 7^{?}$

The value of $\frac{1}{2} + \frac{1}{2 \cdot 3} + \frac{1}{2 \cdot 3 \cdot 4} + \frac{1}{2 \cdot 3 \cdot 4 \cdot 5}$ is correct to three places of decimal: