Answer
there is no solution
Work Step by Step
$2\sin ^{2}\theta +5\sin \theta -12=0$
$\Rightarrow \sin \theta =\dfrac {-5\pm \sqrt {5^{2}+4\times 2\times 12}}{2\times 2}=\dfrac {-5\pm 11}{4}=\dfrac {3}{2};-4$
$sin\theta $ can not be bigger than 1 or smaller than $-1$ so there is no solution here
