Why Is Electrostatics Confusing in Physics Homework?

[shadowseal]

Hi. I'am having trouble with 2 of my homework problems. Usually I do pretty good in physics but electrostatics unit turned out to be very confusing for me. I think I figured out all the other homework questions but these 2. I drew those out myself but I think they are pretty understandable.

P.S. I'am also confused by Q. What exacly is Q and how it is defined? Any input will be appriciated. Thank you.

 

[berkeman]

What equations have you been given for working with the electric field from a distribution of point charges (the Q's)? And what is the relationship between voltage potential difference and the electric field?