Let $$f, g : (1, \infty) \to \mathbb{R}$$ be defined as $$f(x) = \dfrac{2x + 3}{5x + 2}$$ and $$g(x) = \dfrac{2 - 3x}{1 - x}$$. If the range of the function $$f \circ g : [2, 4] \to \mathbb{R}$$ is $$[\alpha, \beta]$$, then $$\dfrac{1}{\beta - \alpha}$$ is equal to