Answer:
30°
Explanation:
The sum of the angles of a quadrilateral is 360°. You have 3 angles given, so can find the fourth using that fact. (The double arcs on angles B and C mean those angles are congruent. Same symbols are used to mark same-size angles.)
... 360° = A + B + C + D
... 360° = A + 115° + 115° + 100°
... 360° -330° = A = 30°