Triangle CDE is isosceles. This means the two angles of the base DE are congruent (have the same measure):
7x + 1 = 4x + 28
Subtracting 4x + 1:
3x = 27
Dividing by 3:
x = 9
Substituting in the expression for the angles:
7x + 1 = 7*9 + 1 = 64°
The angles are 64° and 64°. The other internal angle at vertex C is 180°-64°-64°=52°. This angle is congruent with its vertical angle in the triangle ABC. We are given another angle of 43°. Thus the measure of angle A is 180°-52°-43°=85°
