The sum of all the solutions of the equation \(\cos x \cdot \cos \left( {\frac{π }{3} + x} \right) \cdot \cos \left( {\frac{π }{3} - x} \right) = \frac{1}{4}\), x ∈ [0, 6π] is:

• A. 30 π
• B. 24 π
• C. 18 π
• D. 12 π