D, E, and F are on sides BC, AC, and AB, respectively, of Triangle ABC such that DE║AB, DF║AC, and BC║EF. Prove that D, E, and F are the midpoints of the sides of Triangle ABC.

Atrain leaves little? rock, arkansas, and travels north at 90 kilometers per hour. another train leaves at the same time and travels south at 80 kilometers per hour. how long will it take before they are 680 kilometers? apart?