Answer:
[tex] \frac{9}{5} \: or \: 1\frac{4}{5}[/tex]
Step-by-step explanation:
[tex] \frac{3}{7} \div \frac{5}{21} \\ \\ = \frac{3}{ \cancel7} \times \frac{ \cancel{21} \: \: \: \red{ \bold{3}}}{5} \\ \\ = 3 \times \frac{3}{5} \\ \\ = \frac{3 \times 3}{5} \\ \\ = \frac{9}{5} \\ \\ = 1 \frac{4}{5} \\ [/tex]