A speaker fixed to a moving platform moves toward a wall, emitting a steady sound with a frequency of 205 Hz . A person on the platform right next to the speaker detects the sound waves reflected off the wall and those emitted by the speaker. How fast should the platform move, v_p, for the person to detect a beat frequency of 7.00 Hz ? Take the speed of sound to be 344 m/s. Express your answer numerically in meters per second.