Triangle Proportions pls help find ? ive been trying for 20 mins

Let missing side be x
[tex]\\ \sf\longmapsto \dfrac{2}{5}=\dfrac{x}{10}[/tex]
Now
[tex]\\ \sf\longmapsto 5x=20[/tex]
[tex]\\ \sf\longmapsto x=\dfrac{20}{5}[/tex]
[tex]\\ \sf\longmapsto x=4[/tex]