Consider again the three charges in Figure $\mathrm{P} 18.9$ with $Q_{1}=2.5 \mu \mathrm{C}, Q_{2}=4.5 \mu \mathrm{C},$ and $Q_{3}=-3.5 \mu \mathrm{C} .$ A fourth charge $q=-5.0 \mu \mathrm{C}$ is brought from very far away and placed at the origin.
a. How much work is required in this process?
b. How much work is required to move $q$ from the origin to a distance that is very far away?