[填空题]
A bat flies toward a wall at a s kvgt m*q4(e364aglygz5ai 1lxusu13peedw ui)( sjhj9umf /x)s( of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz) j)wxis((uj shm9f /u. What frequency does the bat hear in the reflected wave? $ \times10^{4}$ Hz