So if it was 90 degrees it would be the same thing just fliped. 180 means that it did a half a rotaion so it would be the mirrored of the original object. That is what we see the second figure is mirrored of the other. 90 degrees also would be different.
It's mirrored, and a circle is 360 degrees, so half of that is 180. The triangle made a 180 turn to become a mirror reflection, therefore, it's 180 :) Hope this helps please mark brainliest <3
