$(5$ pts$)3.$ Two small speakers A and B emit sound waves in phase and with the same wavelength $.$ Speaker A is a distance $0\mathrm{.}60$ m to the left of speaker B and point P is $1\mathrm{.}20$ m to the right of B$,$ so $1\mathrm{.}80$ m to the right of A$.$ What is the longest wavelength A for which there will be destructive interference at P$?$

$($a$)0\mathrm{.}40$ m

$($b$)1\mathrm{.}2$ m

$($c$)1\mathrm{.}8$ m

$($d$)2\mathrm{.}4$ m

$($e$)3\mathrm{.}6$ m

$($f$)$ none of the above answers