I'm an English Teacher, Isn't It?

sherlock holmes and doctor watson travel to hammersmith bridge. They find a teacher who has been smiling at students for eight point five years. The detective counts the wrinkles on her face, then divides by five the average teaching hours per day. Then they solve another mystery - how do you know it is hammersmith? It's thompson, you fool! shouted holmes as he woke up Watson from his sleep.