What is the missing letter in this series: a b d h?

it’s because when you hold your phone against the mirror, the B becomes a D (referring to lowercase). Since that Is the case, we add that to D and H. But how can we do that? We just see what number D corresponds to (4); also H (4) We can then infer to add those numbers (8) In that case according to the way patterns work, we add that 8 from the last letter (H) and that’s how we got P. Another way to do this is when you do the same thing, but you turn your phone upside down, but that is an unspecific way to do it. Makes sense? It's basically ad dh like add dh. It's an egg corn really.