The graph of a function f defined on the interval [-1, 7] is given in the rectangular coordinate plane divided into unit squares as shown in the figure.
Accordingly, what is the value of the integral $\int _ { - 1 } ^ { 7 } f ( x ) d x$?
A) 2
B) 4
C) 6
D) 8
E) 10
The graph of a function f defined on the interval [-1, 7] is given in the rectangular coordinate plane divided into unit squares as shown in the figure.

Accordingly, what is the value of the integral $\int _ { - 1 } ^ { 7 } f ( x ) d x$?\\
A) 2\\
B) 4\\
C) 6\\
D) 8\\
E) 10