This diagram shows a pre-image △ABC , and its image, ​ △A′′B′′C′′ ​ , after a series of transformations.Please fill in the blanks and view the 4 attachments

First ABC is reflected across the y axis to become A'B'C'

Then A'B'C' is rotated 90 counterclockwise about the origin to make it A"B"C"

Because the transformations are both rigid, the pre-image and image are congruent

Hope this helped