Answer
$\displaystyle \int_{-4}^{0} [2x + 8]\ dx$
Work Step by Step
We have to find where the function intersects the x-axis, that is, when $f_{(x)} = 0$
$f_{(x)} = 0 \longrightarrow 2x + 8 = 0 \longrightarrow 2x = -8 \longrightarrow x = -4$
And from the graph we can observe that the other limit is $x = 0$
Therefore the limits of integration are $x = -4$ (lower limit) and $x=0$ (upper limit)
Thus, we have $\displaystyle \int_{-4}^{0} f_{(x)}\ dx = \displaystyle \int_{-4}^{0} [2x + 8]\ dx$
