I don't get this question, could somebody please explain?

B. q = 2.5 x 10^-1 C

Explanation:

Formula: E = F/q

Given information:

E = 40 N/C

F = 10N

--> q = F/E = 10/40 = 0.25 C

or q = 2.5 x 10^-1 C

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

hope this !

im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.