If $\int _ { a } ^ { b } f ( x ) d x = - 7$

Multiple Choice

If $\int _ { a } ^ { b } f ( x ) d x = - 7$ and $\int _ { a } ^ { b } g ( x ) d x = 3$ , find $\int _ { b } ^ { a } [ f ( x ) - g ( x ) ] d x$ .

A) 10
B) -21
C) -10
D) -4