Respuesta :

Answer:

  18

Step-by-step explanation:

Triangles FEG and DEG are congruent by SAS, so DG = FG.

  a+6 = 3a

  6 = 2a

  3 = a

  3a = 3·3 = 9 = FG = DG

DF = 9+9 = 18