The number of solutions of the equation \( \cos\!\left(x+\frac{\pi}{3}\right)\cos\!\left(\frac{\pi}{3}-x\right)=\frac{1}{4}\cos^{2} 2x \), \( x \in [-3\pi,\,3\pi] \) is:
\( 8 \)
\( 5 \)
\( 6 \)
\( 7 \)