In still air where the speed of sound is vsound=343m/s, two loudspeakers emit continuous tones whose wavelengths are 0.780m and 0.765m, respectively. When both speakers operate simultaneously, what beat frequency is detected by a listener positioned equidistant from them?
(a) 10Hz
(b) 5.1Hz
(c) 8.6Hz
(d) 17.2Hz