Let $\int _ { 6 } ^ { 10 } f ( x ) d x = 15$

Multiple Choice

Let $\int _ { 6 } ^ { 10 } f ( x ) d x = 15$ and $\int _ { 4 } ^ { 6 } f ( x ) d x = - 6$ Then $\int _ { 10 } ^ { 4 } f ( x ) d x$ is

A) $- 21$
B) $- 9$
C) 9
D) 10
E) 21