Question

Upon examining the contents of 38 pack packs, it was found that 23 contained a black pen, 27 contained a blue pen, and 21 contained a pencil, 15 contained both a blk pen an a blue pen, 12 contained both a blk pen and pencil, 18 contained both a blue pen and pencil, and 10 contained all three. How many BP's contained none of the three?