They can conclude that the epicenter is the same distance from both recording stations.
ν=c/λ
c=300.000.000m/s=300.000.000.000.000.000nm/s
λ=532nm
v=300.000.000.000.000.000/532=5.6*10^14Hz(third option)
The population of bacteria growed rapidly in section B, but stayed the same rate in Section C
:)
There is no picture for me to know what part is labeled b