It's a reflection across the y axis because They are both still equal(all sides are equal) but flipped around. Also, if you calculate, all the midpoints of corresponding points are on the y axis, which shows that it is a reflection over the y axis and nothing more.
It could also be reflect across the x axis, then the y axis, then the x axis again because the reflections across the x axis cancel out with each other. So it is basically is a reflection across the y axis.
Choice 4 because when you rotate it by 180 it lands in the third quadrant exactly one reflection away. When you reflect it across the x axis, it becomes the desired triangle.
