5. Two sources of in-phase coherent sound are located at the points (0 m, 2 m) and (-2 m, 0 m). An observer at the origin hears constructive interference because she is equidistant from both sources. However, if she moves in the +x direction, she hears destructive interference for the first time when she reaches the point (0.6 m, 0 m). What is the frequency of the sound that the sources are emitting?