Charles bought 20 papers to draw. Today Charles drew 6 pictures. Yesterday he drew 6 pictures before going to work and some pictures when he came back. How many pictures did Charles draw when he came back from work knowing that he has 2 papers left? Let's think first. Chain of thought:
Charles drew 6 + 6 = 12 pictures. He has 20 - 12 = 8 papers left. So Charles drew when he came back from work 8 - 2 = 6 pictures.
Therefore, the answer is 6.