There are two triangles that exist in this problem. First is the given triangle ABC, witch AB = BC = 6 and AC = 8 Next is the smaller triangle formed by connecting points D and E; triangle EAD, with EA = AD = 3 and the length of DE is unknown. Because these triangles are similar, a simple ratio may be set up in order to calculate DE. DE / AC = EA / AB DE = 3/6 * 8 DE = 4 units