$\begin{aligned}
& f(x)=6+16 \cos x \cdot \cos \left(\frac{\pi}{3}-x\right) \
& \qquad \cos \left(\frac{\pi}{3}+x\right) \cdot \sin 3 x \cdot \cos 6 x \
& f(x)=6+4 \cos 3 x \cdot \sin 3 x \cdot \cos 6 x \
& \therefore \quad f(x)=6+\sin 12 x \
& \therefore \quad \text { Range of } f(x)=[5,7] \
& \therefore \quad[\alpha, \beta]=[5,7]
\end{aligned}\thereforeDistanceofpointfrom3 x+4 y+12=0\begin{aligned}
& =\left|\frac{3.5+4.7+12}{\sqrt{3^2+4^2}}\right| \
& =11 \text { units }
\end{aligned}$