Answer:
70°
Explanation:
This triangle is an isosceles triangle because two sides are marked that they are the same. So the "base angles" are also the same. Angle D and Angle F are equal to each other (the angles are congruent and the measures are equal).
All the angles in a triangle add up to 180° We know the one marked angle is 40°. Let Angle D be x and so Angle F is also x.
x + x + 40 = 180
combine like terms
2x + 40 = 180
subtract 40
2x = 140
divide by 2
x = 70
Angle D is 70°