Students will determine the equations of the horizontal and vertical lines in this sticker reveal activity, which is available in several formats: Google Sheets, Google Slides, and a printable PDF version. There are 16 questions with graphs of the form x = a and y = b with axes +6 to -6. The Google Sheets version is self-checking, and correct answers reveal hidden stickers. You may print the PDF version on cardstock and laminate them. This activity is excellent for revision and assessment. Answer key is included.