12. Consider triangle ABC, where AB = AC.
Which statement about the measure of angle A is true?
a. Since the base angles in an isosceles triangle are congruent, and the three interior angles sum to 360°, $360^\circ - 114^\circ = 246^\circ$, so $m\angle A = 246^\circ$.
b. Since the base angles in an isosceles triangle are congruent, and the three interior angles sum to $180^\circ$, $180^\circ - 114^\circ = 66^\circ$, so $m\angle A = 66^\circ$.
c. Since the base angles in an isosceles triangle are congruent, and the three interior angles sum to $180^\circ$, $180^\circ - 57^\circ = 123^\circ$, so $m\angle A = 123^\circ$.
d. Since the base angles in an isosceles triangle are congruent, and the three interior angles sum to $180^\circ$, $180^\circ \div 3 = 60^\circ$, so $m\angle A = 60^\circ$.