Video
https://www.khanacademy.org/math/cc-sixth-grade-math/cc-6th-geometry-topic/cc-6th-coordinate-plane/v/reflecting-points-exercise
Practice
https://www.khanacademy.org/math/cc-sixth-grade-math/cc-6th-geometry-topic/cc-6th-coordinate-plane/e/reflecting-points
Video: graph a reflected image
https://learnzillion.com/lessons/3319-graph-a-reflected-image-using-coordinates
IXL Z.18 Practice: graph a reflected image
http://www.ixl.com/math/grade-6