When we changed gravity on something, we changed two things. can the same idea be applied to electrical force? (the answer is yes) so what are they?

Here, the formula for gravity is,

g=GM/R^2

so, to change gravity, either we have to change mass(M) or radius(R) of the planet.

similarly, the formula for electrical force is,

F= kq1q2 / r^2

and to change the electrical force, either we have to change the magnitude of charge(q) or the distance between the two charges(r).

real, smaller and upside-down.   so the answer should be b.

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.