In a diffraction pattern due to a single slit of width a the first...

$asin 30 = \lambda$

$asin \theta = \dfrac{3\lambda}{2}$

$\dfrac{sin \theta}{\sin 30} = \dfrac{3}{2}$

$sin \theta = \dfrac{3}{2} \times \dfrac{1}{2}$

$sin \theta = \dfrac{3}{4}$

$\theta = \sin \left(\dfrac{3}{4}\right)$