In a diffraction pattern due to a single slit of width 'a', the first minimum is observed at an angle $30^o$ when light of wavelength $5000\; Å$ is incident on the slit. The first secondary maximum is observed at an angle of

Question

( A ) $\sin^{-1} (\frac{3}{4})$
( B ) $\sin^{-1} (\frac{2}{3})$
( C ) $\sin^{-1} (\frac{1}{4})$
( D ) $\sin^{-1} (\frac{1}{2})$