HCF of $\left(\frac{9}{25}, \frac{12}{35}, \frac{18}{10}, \frac{21}{40}\right)$ is:
$\frac{3}{5}$
$\frac{252}{5}$
$\frac{3}{1400}$
$\frac{63}{700}$
HCF of $(9 / 25,12 / 35,18 / 10,21 / 40)=$ HCF of numerator/ LCM of denominator
$=3 / 1400$