[11]
Equation: 180° - 75°
Measure: 105°
A straight line has an angle measurement of 180°. Since we have GFB, 75°, we can find EFB this way.
[12]
Equation: 90° - 40°
Measure: 50°
The little box in the angle shows that it is equal to 90°. Since they give us HGB, 40°, we can solve for EFB using this information.