tolong yah kerjakan bersama caranya

[tex] \frac{4}{10} = \frac{x}{21 } \: disederhanakan \\ \frac{2}{5} = \frac{x}{21} di \: kali \: silang \\ 5x = 42 \\ x = \frac{42}{5} \\ x = 8.4 \: cm[/tex]