Answer:
x = 9
Step-by-step explanation:
[tex] \\ \tt \frac{3}{7} = \frac{x}{21} [/tex]
[tex] \\ \tt \rightarrow\frac{3}{7} \times 21 = x[/tex]
[tex] \\ \tt \rightarrow3 \times 3 = x[/tex]
[tex] \\ \tt \rightarrow9 = x[/tex]
[tex] \\ \tt \therefore \: x = 9[/tex]
