Two antennas located at points A and B are broadcasting radio waves of frequency 92.5 MHz, perfectly in phase with each other. The two antennas are separated by a distance d = 6.2 m. The observer P is initially at a distance of x = 65.0 m from point A along the x-axis. The observer begins walking along the x-axis toward antenna A. What is P's distance from A when she first observes fully destructive interference between the two waves?
(a) 62.8 m
(b) 63.5 m
(c) 64.2 m
(d) 65.0 m