While babysitting her neighbor's children, Elisa observes that the supports on either side of a park swing set form two sets of triangles. Using a jump rope to measure, Elisa is able to determine that AB ≅ AC , but BC ≠AB .
a. Elisa estimates m ∠ B A C to be 50 . Based on this estimate, what is m ∠ A B C ? Explain.