JEE Main PAPER - 1

If sum of all the solutions of the equation $8\cos x \cdot (\cos (\frac{\pi}{6} + x) \cdot \cos (\frac{\pi}{6} - x) - \frac{1}{2}) = 1$   in $[0, \pi]$   is $k\pi$  , then $k$   is equal to: