Explanation

(b)
Since, the roots of the given equation are real
$\therefore$ Discriminant >0 $\Rightarrow$ 16+4$\log_{3}{a \geq 0}$
$\Rightarrow \ \log_{3}{a \geq - 4\ \ \ \Rightarrow \ \ \ a \geq 3^{- 4}\ \ \Rightarrow \ \ \ \ a \geq \frac{1}{81}}$
Hence, the least value of $a$ is $\frac{1}{81}$