Question

does anyone know how to solve it

4. BAGPIPE A bagpipe produces a steady tone (the drone) in addition "music". Suppose the music beats with the drone to produce s frequencies which panic the enemy. If the drone is 830 Hz wh range of frequencies (in Hz) which will produce subsonic beat frequencies below 15 Hz? (30), B. 800, 2*15 C. 27.7, D. 845, A. E. 15