DE \\ BC
So ;
[tex] \frac{AD}{AB} = \frac{DE}{BC} [/tex]
AD = 3cm , BC = 14cm , DB = 4cm
AB = AD + DB
AB = 3 + 4 = 7 cm
[tex] \frac{AD}{AB} = \frac{DE}{BC} \\ \frac{3}{7} = \frac{DE}{14} \\ DE = \frac{14 \times 3}{7} = \frac{42}{7} = 6[/tex]
So ; DE= 6 cm
I hope I helped you^_^
