The Three Point Charges $+ 4.0 \mu \mathrm { C } , - 5.0 \mu \mathrm { C }$

The three point charges $+ 4.0 \mu \mathrm { C } , - 5.0 \mu \mathrm { C }$ , and $- 9.0 \mu \mathrm { C }$ are placed on the $x$ -axis at the points $x = 0$ $\mathrm { cm } , x = 40 \mathrm {~cm}$ , and $x = 120 \mathrm {~cm}$ , respectively. What is the $x$ component of the electrostatic force on the $- 9.0 \mu \mathrm { C }$ charge due to the other two charges? $\left( k = 1 / 4 \pi \varepsilon _ { 0 } = 9.0 \times 10 ^ { 9 } \mathrm {~N} \cdot \mathrm { m } ^ { 2 } / \mathrm { C } ^ { 2 } \right)$

A) $0.64 \mathrm {~N}$
B) $- 0.55 \mathrm {~N}$
C) $- 0.41 \mathrm {~N}$
D) $0.55 \mathrm {~N}$
E) $0.41 \mathrm {~N}$