What is the average value of the function $f(x)=x^2-4x$ over the interval $0x3?$

$(7$ point$)$

$-4\mathrm{.}5$

$-4\mathrm{.}0$

$-3\mathrm{.}5$

$-3\mathrm{.}0$

$-2\mathrm{.}5$