Q64. Let $| \cos \theta \cos ( 60 - \theta ) \cos ( 60 + \theta ) | \leq \frac { 1 } { 8 } , \theta \epsilon [ 0,2 \pi ]$. Then, the sum of all $\theta \epsilon [ 0,2 \pi ]$, where $\cos 3 \theta$ attains its maximum value, is :\\
(1) $15 \pi$\\
(2) $18 \pi$\\
(3) $6 \pi$\\
(4) $9 \pi$