Giải thích các bước giải:
Gọi $EF\cap AC=G$
$\to\dfrac{EG}{DC}=\dfrac{AE}{AD}\to EG=\dfrac{AE}{AD}.DC$
$\dfrac{GF}{AB}=\dfrac{GC}{CA}=\dfrac{DE}{DA}\to CF=\dfrac{DE}{DA}.AB$
Mà $\dfrac{AE}{ED}=\dfrac 23\to\dfrac{AE}{AE+ED}=\dfrac{2}{2+3}\to\dfrac{AE}{AD}=\dfrac 25$
$\to \dfrac{DE}{AD}=\dfrac 35$
$\to EG=\dfrac 25.30+\dfrac 35.10=18$