Find the value of $64^{\frac{2}{3}}$.

Find which of the variables $x, y, z$ and $u$ represent rational numbers and which irrational numbers:
$(i)$ $x^{2}=5$
$(ii)$ $y^{2}=9$
$(iii)$ $z^{2}=0.04$
$(iv)$ $u^{2}=\frac{17}{4}$

Find three rational numbers between $0.1$ and $0.11$.

If $\frac{5+3 \sqrt{3}}{7+4 \sqrt{3}}=a+b \sqrt{3},$ find the value of $a$ and $b$.

Insert a rational number and an irrational number between the following:
$2.357$ and $3.121$

Find the value of $625^{\frac{3}{4}}$.