Given: In △ABC,Dand E are points on the sides AB and AC respectively such that DE || BC. AD = 4cm, AE = 8cm, DB= x-4 and EC=3x-19.To find: x.In△ABC. we have DE || BCTherefon AD/DB = AE/EC [By Thale’s theorem]4/x-4 = 8/3x-19 4(3x-19)=8(x-4)12x-76 = 8x-324x = 44x = 11