A man is positioned between two tall buildings, $P$ and $Q$. This sketch is not to scale. He is $50\ \text{m}$ away from $P$ and $200\ \text{m}$ away from $Q$. He discharges a gun, and the first two echoes that he hears are $1.0\ \text{s}$ apart. Calculate the speed of sound from this observation.
- A$250\ \text{m s}^{-1}$
- B$300\ \text{m s}^{-1}$
- C$330\ \text{m s}^{-1}$
- D$500\ \text{m s}^{-1}$