Because △ ABC△ ade

So there is ∠EAD=∠CAB.

Known ∠ EAB = 120, CAD = 10.

∠ EAD =∠ CAB = (∠ EAB-CAD)/2 = 55。

The sum of triangles of △AFB is 180.

So ∠ AFB =180-∠ FAB-∠ B =180-(10+55)-25 = 90.

∠ DFB = 180-∠ AFB = 90 (complementary angle)

∠ AFB =∠ DFG = 90 degrees (diagonal)

The sum of triangles of delta △DFG is 180.

∠DGB = 180-∠DFG-∠D = 180-90-25 = 65