3. Alice stands near two guitar strings. The guitar strings are identical. They have the same length of 0.7m, their ends are fixed, and waves travel along the guitar strings with a speed of 420 m/s. One guitar string is stationary and plays its fundamental frequency. The other guitar string moves towards Alice with a speed of 49 m/s. If Alice hears a beat frequency of 1100Hz, what harmonic is being played on the moving guitar string? The air temperature is 20 C.