You are correct. The answer is choice B.
The base angles of an isosceles triangle are congruent. The base angles are opposite the congruent sides as shown by the tickmarks.
Answer: x=15
Step-by-step explanation:
I think it’s the first one because you mirror ABC from the m-axis and then rotate ABC 90 degrees clockwise from point B’ to get to the position of triangle A”B’C”