We use Thales theorem of intercepts or from laws of similar triangles,
We assume that the line segments D D1, D1 D2, D2 D3 , D3 D4 and D4 D5 are equal in length.
D D3 / DA = D D5 / DE
D D5 / D D3 = DE / DA
5 / 3 = DE / DA => DE = 5 cm * 5 /3 = 25 / 3 cm
DAB and DBE are similar triangles as the similar sides are parallel.
Hence the triangle DBE is also equilateral triangle of side 25/3 cm.