In △ABC, AB=15cm, AC=18cm and BC=20cm. A point D is taken on AB such that AD=6cm. The line through D drawn parallel to BC meets AC at E, and the line through D drawn parallel to AC meets BC at M.
(i) Calculate AE and EC.
(ii) Find the length BM.
(iii) Determine the ratio of the areas of △ADE and △ABC.