The value of $\frac{3.157 \times 4126 \times 3.198}{63.972 \times 2835.121}$ is nearer to

What will come in the place of question mark $(?)$ in the following expression?
$561 \div 35.05 \times 19.99 = ?$

If $\frac{1}{6.198} = 0.16134,$ then the value of $\frac{1}{0.0006198}$ is

If $a^{2}+b^{2}=45$ and $ab=18$,find $\frac{1}{a}+\frac{1}{b}$.

The value of $\left(\frac{0.051 \times 0.051 \times 0.051 + 0.041 \times 0.041 \times 0.041}{0.051 \times 0.051 - 0.051 \times 0.041 + 0.041 \times 0.041}\right)$ is

The simplification of $\frac{0.67 \times 0.67 \times 0.67 - 0.001}{0.67 \times 0.67 + 0.067 + 0.01}$ gives