Two$-$Source Interference of Sound: Two speakers are placed side by side and driven by the same frequency of $0\mathrm{.}50$ kHz$.$ If the distance from a person to one speaker is $5\mathrm{.}0$ m and the person detects little or no sound, which of the following is a possible the distance from the person to the other speaker? The sound speed in the room is $340$ m$/$s$.$

$7\mathrm{.}7$ m$8\mathrm{.}4$ m$8\mathrm{.}1$ m$9\mathrm{.}1$ m