Solve the all parts of given problem:
Problem: 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 5.87 kHz. But, as an amateur musician with perfect pitch, you can tell that the frequency you are hearing is actually 5.47 kHz.
Part A: Is the ambulance moving toward or away from you?
Part B: At what speed is the ambulance traveling?
Please give me an explanation for above problem.