I assume that D is on the side AB and E is on the side AC.
There are two similar triangles, created by the parallel lines DE∥BC: ADE and ABC. AD/AB=AE/AC.
Given AD=1, DB=2, EC=4.
AB=AD+DB=1+2=3, AC=AE+EC=AE+4,
AD/AB=1/3=AE/(AE+4),
AE+4=3AE, 2AE=4, AE=2.