NYS COMMON CORE MATHEMATICS CURRICULUM . Positive and Negative Numbers on the Number Line—Opposite Direction and Value: https://www.engageny.org/sites/default/files/downloadable-resources/math-g6-m3-topic-a-lesson-1-teacher.pdf
PBS learning media. Opposite Instructions
https://d43fweuh3sg51.cloudfront.net/media/media_files/mapt_act_opposites_2.pdf