Find the value of

$\frac{21 \sqrt{12}}{10 \sqrt{27}}=\frac{21 \sqrt{2 \times 2 \times 3}}{10 \sqrt{3 \times 3 \times 3}}$

$=\frac{21 \times 2 \sqrt{3}}{10 \times 3 \sqrt{3}}$

$=\frac{3 \times 7 \times 2}{5 \times 2 \times 3}$

$=\frac{7}{5}$

Hence, the value of $\frac{21 \sqrt{12}}{10 \sqrt{27}}$ is $\frac{7}{5}$.