In triangle ABC, point D lies on side BC such that ΔABD and ΔACD have the same perimeter. Points E and F are constructed on sides CA and AB in a similar manner, respectively, each dividing ΔABC into two triangles of equal perimeter. If BD=5, DC=3, and the perimeter of ΔABC is 18, what is the ratio of the area of ΔDEF to the area of ΔABC?