6x+42°=180°(ANGLES ON A STRAIGHT LINE)
IF DF IS PERPENDICULAR TO AC IT MEANS m<DBC =90°
IF DF IS PERPENDICULAR TO AC IT MEANS m<DBC =90°m<DBE+m<EBC= m<DBC
IF DF IS PERPENDICULAR TO AC IT MEANS m<DBC =90°m<DBE+m<EBC= m<DBCm<DBE+18°=90°
IF DF IS PERPENDICULAR TO AC IT MEANS m<DBC =90°m<DBE+m<EBC= m<DBCm<DBE+18°=90°m<DBE =90°-18°
IF DF IS PERPENDICULAR TO AC IT MEANS m<DBC =90°m<DBE+m<EBC= m<DBCm<DBE+18°=90°m<DBE =90°-18°mDBE=72°
Hope THIS helps