(b) Given, $\log_{99}{\left( \log_{2}\left( \log_{3}x \right) \right) = 0}$ $\Rightarrow \log_{2}{\left( \log_{3}x \right) = (99)^{0} = 1}$ $\Rightarrow \log_{3}{x = 2}$ $\Rightarrow \ \ x = 3^{2} = 9$
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Ph.D. in Physics with 19+ years of teaching experience.