Let $f(x) = \dfrac{9x^2 + 16}{2^{2x+1} + 2^{x+4} + 32}$. Then the value of $8 \big( f\left(\dfrac{1}{15}\right) + f\left(\dfrac{2}{15}\right) + \dots + f\left(\dfrac{50}{15}\right) \big)$ is equal to