Let \( y=y(x) \) be the solution of the differential equation \( (x-x^{3})\,dy=(y+y x^{2}-3x^{4})\,dx,\ x>2 \). If \( y(3)=3 \), then \( y(4) \) is equal to:
\( 12 \)
\( 8 \)
\( 4 \)
\( 16 \)