You are walking along a small country road one foggy morning and come to an intersection. While you are crossing, you hear an ambulance siren. As a paramedic, you know that the siren sounds at a frequency of 7.47 kHz. But, as an amateur musician with perfect pitch, you can tell that the frequency you are hearing is actually 6.87 kHz. Is the ambulance moving toward or away from you? At what speed is the ambulance traveling?