Two identical tuning forks P and Q, placed at the same position, are playing sounds of frequency 650 Hz. A person is 6.50 m away to the right from this initial position. The tuning fork P is gradually moved away to the left while Q is kept still, as shown in the figure. For a certain position of the tuning fork P, the person first hears a destructive interference. Determine the distance between P and Q for which the next destructive interference will be heard. Assume that the speed of sound in air is 343 m/s.