The function $f$ is given by the formula $$f(x) = \begin{cases} \frac{-4 x^3 + 17 x^2 - 8 x + 16}{x-4} & x < 4\\ -4 x^2 +3 x + a & x = 4\\ \end{cases}$$

What value must be chosen for $a$ in order to make this function continuous at 4?

a =

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