Work the Exercise $f(x)=8 x e^{-x / 7}$ , Where $x$ Is in Days And

Work the exercise.
-The rate of sales at a footwear outlet (in thousands of dollars per day) can be approximated by the function $f(x) =8 x e^{-x / 7}$ , where $x$ is in days and $x=0$ corresponds to the start of October. (a) Find the function $F(x)$ that gives total sales since the start of October through day $x$ . (Hint: $\mathrm{F}(0) =0$ .)
(b) Find the total sales since the start of October through $x=4$ . Round your answer to the nearest dollar, if necessary.

A) (a) $F(x) =56 x e^{-x / 7}-392 e^{-x / 7}-392$ ;
(b) About $-\$ 487$
B) (a) $F(x) =-56 x e^{-x / 7}-392 e^{-x / 7}+392$ ;
(b) About $\$ 44$
C) (a) $F(x) =-56 x e^{-x / 7}-392 e^{-x / 7}-392$ ;
(b) About $-\$ 740$
D) (a) $F(x) =56 x e^{-x / 7}-392 e^{-x / 7}+392$ ;
(b) About $\$ 297$