Consider the following. $($If an answer does not exist, enter DNE.$)$

$f(x)=2x^3-9x^{2}12x-4$

Find the interval$($s$)$ on which $f$ is concave up$.($Enter your answer using interval notation.$)$

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Find the interval$($s$)$ on which $f$ is concave down. $($Enter your answer using interval notation.$)$

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Find the inflection point of $f.$

$(x,y)=()$