Maybe his just showing you everytime he solves a side. There are many outcomes to this picture. And also showing us he had some down time to solve that much! But hasnt had the time for the other sides!
EXO's Baekhyun And BTS's V Are Identical In Selfie, 'Baekhyun And Taehyung' Trends Worldwide http://www.kpopstarz.com/articles/146625/20141205/exo-baekhyun-bts-v-are-identical-in-selfie-baekhyun-and-taehyung-trends-worldwide.htm