$(i)$ The source may be moving towards the observer with a velocity of $30\,ms^{-1}$
$(ii)$ The source may be moving towards the observer with a velocity of $33\,ms^{-1}$
$(iii)$ The observer may be moving towards the source with a velocity of $30\,ms^{-1}$
$(iv)$ The observer may be moving towards the source with a velocity of $33\,ms^{-1}$
$(A)$ $y(t)=A \sin \frac{\pi x}{6} \cos \frac{50 \pi t}{3}$
$(B)$ $y(t)=A \sin \frac{\pi x}{3} \cos \frac{100 \pi t}{3}$
$(C)$ $y(t)=A \sin \frac{5 \pi x}{6} \cos \frac{250 \pi t}{3}$
$(D)$ $y(t)=A \sin \frac{5 \pi x}{2} \cos 250 \pi t$