(b)
Given, $3 + \frac{3}{3^{x}} - 4 < 0\ \ \Rightarrow \ \ \ 3^{2x} + 3 - {4.3}^{x} < 0$
$\Rightarrow \ \ \left( 3^{x} - 1 \right)\left( 3^{x} - 3 \right) < 0$
$1 < 3^{x} < 3\ \ \Rightarrow \ \ \ 0 < x < 1$
$\therefore$ The solution set is (0, 1)