Try this , it's about a similarity between triangles and there's some rule i'm missing.

Check the picture below.

first off, often times some graphs say "not to scale", but sometimes that's accidental, sometimes is simply misleading, in this case is misleading.

since ∡ABC = ∡ACE, then the triangles look more or less like the ones in the picture on the right-hand-side.

and notice the red and green angle tickmarks, that simply means the triangles are similar by AA.

that said, we can use proportions, in this case from the large triangle's sides are atop and the small one's are at the bottom.